# Teaching and learning plan on introduction to quadratic equations

```Teaching & Learning Plans
Junior Certificate Syllabus
The Teaching & Learning Plans
are structured as follows:
Aims outline what the lesson, or series of lessons, hopes to achieve.
Prior Knowledge points to relevant knowledge students may already have and also
to knowledge which may be necessary in order to support them in accessing this new
topic.
Learning Outcomes outline what a student will be able to do, know and understand
having completed the topic.
Relationship to Syllabus refers to the relevant section of either the Junior and/or
Leaving Certificate Syllabus.
Resources Required lists the resources which will be needed in the teaching and
learning of a particular topic.
Introducing the topic (in some plans only) outlines an approach to introducing the
topic.
Lesson Interaction is set out under four sub-headings:
i.
Student Learning Tasks – Teacher Input: This section focuses on possible lines
of inquiry and gives details of the key student tasks and teacher questions which
move the lesson forward.
ii.
Student Activities – Possible Responses: Gives details of possible student
reactions and responses and possible misconceptions students may have.
iii. Teacher’s Support and Actions: Gives details of teacher actions designed to
support and scaffold student learning.
iv. Assessing the Learning: Suggests questions a teacher might ask to evaluate
whether the goals/learning outcomes are being/have been achieved. This
evaluation will inform and direct the teaching and learning activities of the next
class(es).
Student Activities linked to the lesson(s) are provided at the end of each plan.
Teaching & Learning Plan:
Junior Certificate Syllabus
Aim
• To enable students recognise quadratic equations
• To enable students use algebra, graphs and tables to solve quadratic
equations
• To enable students form a quadratic equation to represent a given problem
• To enable higher-level students form quadratic equations from their roots
Prior Knowledge
Students have prior knowledge of:
• Simple equations
• Natural numbers, integers and fractions
• Manipulation of fractions
• Finding the factors of x2 + bx + c where b, c ∈ Z
• Finding the factors of ax2+ bx + c where a, b, c ∈ Q, x ∈ R (Higher Level)
• Patterns
• Basic algebra
• Simple indices
• Finding the factors of x2 − a2
Learning Outcomes
As a result of studying this topic, students will be able to:
• understand what is meant by a quadratic equation
• recognise a quadratic equation as an equation having as many as two
solutions that can be written as ax2 + bx + c = 0
• represent a word problem as a quadratic equation and solve the relevant
problem
• form a quadratic equation given its roots
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1
Teaching & Learning Plan: Quadratic Equations
Catering for Learner Diversity
In class, the needs of all students, whatever their level of ability level, are equally
important. In daily classroom teaching, teachers can cater for different abilities by
providing students with different activities and assignments graded according to levels
of difficulty so that students can work on exercises that match their progress in learning.
Less able students, may engage with the activities in a relatively straightforward way
while the more able students should engage in more open–ended and challenging
activities.
In interacting with the whole class, teachers can make adjustments to suit the needs of
students. For example, more challenging material similar to that contained in Question
11 in Section A: Student Activity 1 can be provided to students where appropriate.
Apart from whole-class teaching, teachers can utilise pair and group work to encourage
peer interaction and to facilitate discussion. The use of different grouping arrangements
in these lessons should help ensure that the needs of all students are met and that
students are encouraged to verbalise their mathematics openly and to share their
learning.
Relationship to Junior Certificate Syllabus
Topic Number
Description of topic
4.7 Equations
Using a variety of
and
problem solving
inequalities strategies to solve
equations and
inequalities. They
identify the necessary
information,
represent problems
mathematically, making
correct use of symbols,
words, diagrams, tables
and graphs.
© Project Maths Development Team 2011
Learning outcomes
Students should be able to
–– solve quadratic equations of the
form
x2 + bx + c where b, c ∈ Z
and
x2 + bx + c
is factorisable
ax2+ bx + c where a, b, c ∈ Q,
x ∈ R (HL only)
whole number roots (HL only)
–– solve simple problems leading to
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2
Teaching & Learning Plan: Quadratic Equations
Lesson Interaction
Teacher Input
Student Activities: Possible Responses
Teacher’s Support and
Actions
Assessing the
Learning
Section A: To solve quadratic equations of the form (x-a)(x-b) = 0 algebraically
»» What is meant by finding the
solution of the equation 4x +
6 = 14?»
• We find a value for x that makes the
statement (that 4x + 6 = 14) true
»
»» Why is x =1 not a solution of
4x + 6 = 14
• Because 4(1) + 6 ≠ 14
»
»» How do we find the solution
to 4x + 6 = 14?
»» Remember to check your
»» Write 4x + 6 = 14 on the
board.»
»» Ask students to write the
solution on the board.
Teacher Reflections
»» Do students
remember what is
meant by solving
an equation?»
»» Can students see
why »
x =1 is not a
solution?»
• Students write the solution in their copies.
-6
-6
4x + 6 = 14
4x = 8
÷4
÷4
x=2
»» Do students know
how to check their
or
4x + 6 = 14
4x + 6 - 6 = 14 -6
4x = 8
x=2
4 (2) + 6 = 14 True
»»
»»
»»
»»
»»
What is 4 x 0?
What is 5 x 0?
What is 0 x 5?
What is 0 x n?
What is 0 x 0?»
»» When something is multiplied
by 0 what is the answer?
© Project Maths Development Team 2011
•
•
•
•
•
0
0
0
0
0»
»» Write the questions and
solutions on the board.
4x0=0
5x0=0
0x5=0
0xn=0
0x0=0
»» Do students
understand that
multiplication by
zero gives zero?
• 0
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Teaching & Learning Plan: Quadratic Equations
Teacher Input
»» If xy = 0 what do we
know about x and or y?
Student Activities: Possible
Responses
• x = 0 or y = 0 or both are equal
»» Compare»
(x - 3)(x - 4) = 0, with
xy = 0 and what
information can we
arrive at?»
•
to 0.»
»» If x - 3 = 0, what does this • x = 3
»
x=4
»» How do we check if »
x = 3 is a solution to
(x - 3)(x - 4) = 0?
• Insert x = 3 into the equation
and check if we get 0.»
»
»» How do we check if »
x = 4 is a solution to
(x - 3)(x - 4) = 0?
• Insert x = 4 into the equation
and check if we get 0.
»» Write in your copies in
words what x = 3 or x= 4
means in the context of
(x - 3)(x - 4) = 0.
• Students write in words in their
copies what this means and
discuss with the student beside
them.
»» When an equation is
written in the form»
(x - a) (x - b) = 0, what
are the solutions?
•
© Project Maths Development Team 2011
board.»
x - 3 = 0 or x - 4 = 0 or both are »» Allow students to
equal to 0.»
»
»
»
»» If x - 4 = 0, what does this •
Teacher’s Support and
Actions
»» Write xy = 0 on the
x = a or x = b
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discuss and compare
Assessing the Learning
»» Can students find the
solution to (x - 3) (x - 4) = 0?
Teacher Reflections
»» Do students understand
what is meant by the
solution to this equation?
»» Write on the board:»
xy = 0
(x - 3) (x - 4) = 0
x - 3 = 0 or x - 4 = 0
x = 3 or x = 4
»» Write on the board:»
(3 - 3) (x - 4) = 0
0(x - 4) = 0
0 = 0»
»» Write on the board:»
(x - 3) (4 - 4) = 0
(x - 3) 0 = 0
0=0
»» Can students write in words
what x = 3 and x = 4 means?
»» Write on the board:»
(x - a)(x - b) = 0
x-a=0x-b=0
x=a x=b
»» Can students generalise the
solution to (x - a)(x - b) = 0?
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Teaching & Learning Plan: Quadratic Equations
Student Learning Tasks: Teacher Student Activities: Possible
Input
Responses
»» Solve (x - 1)(x - 3) = 0
• (x - 1) (x - 3) = 0
»
(x - 1) = 0 or (x - 3) = 0
»
x = 1 or x = 3.
»
»
»
»
»
Teacher’s Support and Actions Assessing the Learning
»» Write the solution on the
board.
»» Can students detect
that if an equation
is of the form (x − a)
(x−b) = 0, then x = a
and x = b are both
solutions?
»» Distribute Section A: Student
Activity 1
»» Are students able to
solve equations of
the form »
(x - a) (x - b) = 0?
(1 - 1) (x - 3) = 0
(1 - 1) (x - 3) = 0
0 (x - 3) = 0
0 = 0»
»» How do we check that these
are solutions?»
»
»
Teacher Reflections
• (x - 1) (3 - 3) = 0
(x - 1) 0 = 0
0 = 0»
True»
»» Is it sufficient to state x = 3 is a • No, both x = 3 and x = 1 are
solution to»
solutions.
(x - 1) (x - 3) = 0?
»» Answer questions 1 to 11 on
Section A: Student Activity 1.
»» If students are unable to
make the jump from »
(x - a) (x - b) = 0 to
(x + a) (x + b) = 0.
»» If students are having
difficulty, allow them to
talk through their work so
that misconceptions can be
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Teaching & Learning Plan: Quadratic Equations
Student Activities: Possible
Input
Responses
»» How does the equation x (x - 5) = 0 • It is the same.»
»
»
differ from the equation»
(x - 0)(x - 5) = 0?
»» Why are they the same?»
»
• Because x and x - 0 are the
same, i.e. x = x - 0.
»» Hence what is the solution?
•
»» What are the solutions of »
x (x - 6) = 0?
•
»» Answer questions 12-16 on Section
A: Student Activity 1.
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x = 0 or x = 5
x = 0 and x = 6
Teacher’s Support and
Actions
Assessing the
Learning
»» Write on the board:»
x (x - 5) = 0 and
(x - 0) (x - 5) = 0
x = 0 and x - 5 = 0
x = 0 or 5
0 (x - 6) = 0 True
x (6 - 6) = 0 True
Teacher Reflections
»» Write on the board:»
x (x - 6) = 0
x = 0 and x - 6 = 0
x = 0 or 6
0 (x - 6)= 0 True
x (6 - 6) = 0 True
»» Do students
recognise that the
solutions to »
x(x-a) = 0
are x= 0 and x = a?
»» On completion of
questions 12-16
those students who
need a challenge can
be encouraged to
do question 17 on
Section A Student
Activity 1.
»» Can students solve »
x (x - a) = 0?
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Teaching & Learning Plan: Quadratic Equations
Input
Student Activities: Possible
Responses
Teacher’s Support and
Actions
Assessing the
Learning
Section B: To solve quadratic equations of the form (x - a) (x - b) = 0
making use of tables and graphs
»» Equations of the form »
ax2 + bx + c = 0 are given a
special name, they are called
»» Give me an example of a
»» Is (x - 1) (x - 2) = 0 a Quadratic
Equation?
»» Why is (x - 1) (x - 2) = 0
»» Write ax2 + bx + c = 0 and
board.»
• 2x2 + 3x + 5 = 0
that the students list do not
• Yes»
have to be factorisable ones at
the moment and special cases »
• Because when you multiply it
ax2 + bx = 0
2
out you get x - 3x + 2 = 0, which ax2 + c = 0
is in the format ax2 + bx + c = 0. will be dealt with later.
»» What does it mean to solve the
equation (x - 1) (x - 2) = 0?
• Find values for x that makes this
statement true.»
»» What is meant by the roots of
an equation?»
»
• The roots of an equation are
the values of x that make the
equation true.»
• (x - 1) (x - 2 ) = 0
x - 1 = 0 or x - 2 = 0
x = 1 or x = 2
(1 - 1) (x - 2) = 0 True
(x - 1) (2 - 2) = 0 True
»» So what are the roots of »
(x - 1) (x - 2) = 0
•
© Project Maths Development Team 2011
»» Do students
recognise a
Equation?»
»» Do students
understand
equations can be
written in the form»
(x - a) (x - b)=0?
»» Can students solve
equations of the
form »
(x - a) (x - b) = 0?
»» Do students
understand that
finding the roots
of an equation
and solving an
equation are the
same thing?
»» It is true that finding the roots
• Yes»
of an equation and solving the
»
equation mean the same thing?»
»
»» Solve the equation»
(x - 1) (x - 2) = 0 using algebra.
»
»
»
Teacher Reflections
x = 1 and x = 2.
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Teaching & Learning Plan: Quadratic Equations
Student Activities: Possible
Responses
»» Copy the table on the board into your
exercise book and complete it.»
»
»
»
»
»
»
»
»» For what values of x did
(x - 1)(x - 2) = 0?
•
x
(x - 1) (x - 2)
-2
12
-1
6
0
2
1
0
2
0
3
2
x = 1 and x = 2
Teacher’s Support and
Actions
Assessing the
Learning
»» Display the following
table on the board:
»» Are students able
to complete the
the table the
values of x when
(x - 1) (x - 2) = 0
and hence solve
the equation?
x
(x - 1) (x - 2)
-2
-1
0
1
Teacher Reflections
2
3
»
»» What name is given to the value(s) of x • Solution(s) or roots.
that make(s) an equation true?
»» Draw a graph of the information in
the table, letting y = (x - 1) (x - 2).
»» For what values of x did the graph cut
the x axis?
»» What is meant by the solution of an
equation?»
»» What was the value of y =(x - 1)(x - 2)
when x = 1 and x = 2?
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»» Draw the graph on the
board
•
»» Are students
able to draw the
from the graph
the values of x
when »
(x - 1) (x - 2) = 0?
x = 1 and x = 2
»
• The equation is true for
the value of x.
• 0
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Teaching & Learning Plan: Quadratic Equations
Teacher Input
Student Activities: Possible
Responses
Teacher’s Support
and Actions
Assessing the Learning
»» When using algebra to solve,
what were the values of x for
which (x - 1) (x - 2) = 0 called?
• Solutions, roots»
»
»
»» Write the student's
board.
»» How can we get the solution
by looking at the table?»
• When (x - 1) (x - 2) has the
value zero.»
»» How can we get the solution
by looking at the graph?
• Where it cuts the x axis or
where the y value is zero
»» Do students understand
that:
• solving the equation
using algebra
• finding the value of
x when the equation
equals zero in the
table
• finding where the
graph of the function
cuts the x axis
are all methods of
finding the solution to
the equation?
»» Complete the exercises in
Section B: Student Activity 2.
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Teacher Reflections
»» Distribute Section B.
Student Activity 2.
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Teaching & Learning Plan: Quadratic Equations
Input
Student Activities: Possible
Responses
Teacher’s Support and
Actions
Assessing the
Learning
Section C: To solve quadratic equations of the form x2 + bx + c = 0
that are factorable
»» What does it mean to find the
factors of a number?»
• Rewriting the number as a product »» Write on the board:»
of two or more numbers.»
x2 + 3x + 2 = 0
a =1, b =3, c =2
»» What does it mean to find the
• It means to rearrange an algebraic
Guide number =1 x 2 = 2»
factors of x2 + 3x + 2?
expression so that it is a product of
»
its prime factors.»
»» Write on the board 1 x 2 =
2 and -1x - 2 = 2.
»» What is the Guide number of this • 2»
equation?»
»
»» Write on the board:»
x2 + 3x + 2 = 0
»» How did you get this Guide
• Multiplied 1 x 2 because
x2 + 2x + 1x + 2 = 0
number?»
comparing this equation to the
»
form ax2 + bx + c = 0, a = 1 and c
»» Write on the board»
»
= 2.»
x2 + 1x + 2x + 2 = 0
»» What are the factors of 2?»
• 1 and 2 or -1 and -2»
»» Which pair shall we use?»
»
»» Why would I not use the pair -1
and -2?»
»
»» Ask students if this looks familiar
to any other type of factorising
they have done before?»
»» Could I have written 1x plus 2x
© Project Maths Development Team 2011
»» Allow students to compare
their work.»
• 1 and 2 because added together 1x
+ 2x gives us +3x.
»» Ask two students to come
to the board and write
• They would give you -3x which
down their solution to»
is not a term in the original
x2 + 2x + 1x + 2 = 0
equation.»
and»
x2 + 1x + 2x + 2 = 0
• This is Factorising by Grouping»
»
»
Teacher Reflections
»» Do students
understand the
Guide number
method of
finding the
factors of a
»» Can students find
the factors of a
simple equation?»
»» Do students
understand why
they should use 1
and 2?»
»» Can students
connect this
to their prior
knowledge of
Factorising by
Grouping?
• Students work on factorising each.
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Teaching & Learning Plan: Quadratic Equations
Student Learning Tasks: Teacher Student Activities:
Input
Possible Responses
»» I want you to investigate this
for yourselves by Factorising
by grouping each of these»
x2 + 2x + 1x + 2 = 0
x2 + 1x + 2x + 2 = 0
»
Teacher’s Support and Actions
Assessing the Learning
• One student writes on
board:»
x2 + 2x + 1x + 2 = 0
x(x + 2) + 1(x + 2) = 0
(x + 1) (x + 2) = 0
x = -1 or x = -2
Teacher Reflections
»» Why does the first solution
• Another student writes
have (x+2) in each bracket and
on the board:»
the second solution have (x+1)
x2 + 1x + 2x + 2 = 0
in each bracket?»
x(x + 1) + 2(x + 1)
(x + 2) (x + 1) = 0
»» How would you check that
x = -2 or x = -1
both are correct?
• (x + 1) (x + 3) = 0
x + 1 = 0 or x + 3 = 0
x = -1 or x = -3
(-1 + 1) (x + 3) = 0 True
(x + 1) (-3 + 3) = 0 True
»» Solve the equation:»
x2 + 4x + 3 = 0
»» Answer questions 1 - 8 on
Section C: Student Activity 3.
»» Write the solution on the board. »» Are students able to
factorise the equation
and hence solve it?
»» Distribute Section C: Student
Activity 3.
»» Circulate and see what answers
the students are giving and
»» Can students factorise
an expression of the
form and solve an
equation of the form»
x2 + bx + c = 0?
»» Ask individual students to write
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Teaching & Learning Plan: Quadratic Equations
Teacher Input
»» The width of a rectangle
is 5cm greater than its
length. Could you write
this in terms of x?
Student Activities:
Possible Responses
• x (x + 5)
»
»
»
Teacher’s Support and Actions
Assessing the Learning
»» Get the students to draw
a diagram of a suitable
rectangle.»
»» Are students extending
their knowledge of
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»» Allow students to adopt an
explorative approach here
before giving the procedure.»
»» If we know the area is
equal to 36cm2, write the
information we know
equation.»
• A = (length) (width)»
x (x + 5) = 36
»
»
»
»» Solve this equation.»
»
»
»
»
»
•
»» What is the length and
width of the rectangle?»
»
• The length is equal to
4cm and width is equal
to 9cm.»
»» Do students understand
why x = -9 was a spurious
solution?»
»» Is it sufficient to leave this
question as x = 4?
• No. You must bring it
back to the context of
the question.
»» Do students understand
that saying x = 4 is not
the question, but that it
must be bought back into
context of the question?
© Project Maths Development Team 2011
x2 + 5x - 36 = 0
(x + 9) (x - 4) = 0
x+9=0x-4=0
x = -9 or x = 4
(-9 + 9) (x - 4) = 0 True
(x + 9) (-4 - 4) = 0 True
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»» Ask a student to write
the solution on the board
explaining what they are
doing in each step.»
»» Challenge students to explain
why x= -9 is rejected.
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Teacher Reflections
12
Teaching & Learning Plan: Quadratic Equations
Teacher Input
Student Activities:
Possible Responses
»» Complete the remaining
exercises on Section C:
Student Activity 3.
Teacher’s Support and Actions
Assessing the Learning
»» Teacher may select a number of
these questions or get students
to complete this activity sheet
for homework.»
problems posed in the student
activity?
Teacher Reflections
»» Ask individual students to do
questions on the board when
the class has done some of the
work. Students should explain
their reasoning in each step.
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Teaching & Learning Plan: Quadratic Equations
Student Learning
Student Activities: Possible
Responses
Teacher’s Support and Actions
Assessing the Learning
Section D: To solve quadratic equations of the form ax2 + bx + c that are
factorable (Higher Level only)
Teacher Reflections
»» Solve the equation» • 2x2 + 5x + 2 = 0
»» Ask a student to come to the board and »» Do students understand that »
2
2x + 5x + 2 = 0.
explain how they factorised this.
2x2 + 5x + 2 = (2x + 1) (x + 2)?
Guide number is: 4 [coefficient
2
2x + 4x +1x + 2 = 0
of x2 and 2 the constant]
2x (x + 2) + 1 (x + 2) = 0
2 x 2 = 4»
(2x + 1) (x + 2) = 0
Factors of 4 are 4 x 1 or 2 x 2»
2x + 1 = 0 or x + 2 = 0
x = -1/2 or x = -2
• Use 4 x 1 because this gives
or
you a sum of 5»
2x2 + 1x +4x + 2 = 0
»
x (2x + 1) + 2 (2x + 1) = 0
2x2 + 4x +1x + 2 = 0
(x + 2) (2x + 1) = 0
2x (x + 2) + 1 (x + 2) = 0
x + 2 = 0 or 2x + 1 = 0
(2x + 1) (x + 2) = 0
x = -2 or x = -1/2
2x + 1 = 0 or x + 2 = 0
x = -1/2 or x = -2
»» Find the factors of » • (3x + 1)(x + 1)
3x2 + 4x +1 and
»
hence solve »
3x + 1 = 0 x + 1 = 0
2
3x + 4x +1 = 0
3x = -1 x = -1
x= -⅓ x = -1
contained in
Section D: Student
Activity 4.
»» Circulate and see what answers the
students are giving and address any
misconceptions.
»» Distribute Section D: Student Activity 4. »» Can students factorise
expressions of the form»
»» Circulate and check the students’ work
ax2 + bx + c and hence solve
ensuring that all students can complete
equations of the form»
ax2 + bx + c = 0?
»» Ask individual students to do questions
on the board when some of the work
is done using the algorithm, table and
graph.
© Project Maths Development Team 2011
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»» Can students solve equations
of the form ax2 + bx + c = 0
by algorithm, table and
graphically?
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14
Teaching & Learning Plan: Quadratic Equations
Input
Student Activities: Possible
Responses
»» Are x2 + 6x + 5 = 0 and x2 + 6x = 0
»
• Yes because the highest power
of the unknown in these
examples is 2.»
»» Give a general definition of a
•
»» Are ax2 + c = 0?
ax2 + bx = 0
• Yes, because the highest power
of the unknown is still 2.»
»
»» Do you have a quadratic equation if
a = 0? If not what is it called?
• No, because the highest power
is no longer 2. This is called a
linear equation.
Teacher’s Support and
Actions
Assessing the
Learning
Section E: To solve quadratic equations of the form x2 - a2 = 0
»» What would the general form of the
equation look like if»
(i) b = 0,
(ii) c = 0,
(iii) a = 0,
(iv) b = 0 and c = 0?
»» Do students
all take the form»
ax2 + bx + c = 0 and
b and/or c can be
zero
ax2 + bx + c = 0.
»
•
•
•
•
»» Do students
understand the
difference between
linear equation?
ax2 + c = 0
ax2 + bx = 0
bx + c = 0
ax2 = 0
»» So is x2 - 16 a quadratic expression?
»
• Yes, because the highest power »» Give students time to
of the unknown is 2.»
find the factors.»
»» What are the factors of x2 - 16?
• (x + 4) (x - 4)
• The difference of two squares.»
»» What is the solution of x2 - 16 = 0?
•
»» How can we prove these values are
the factors of x2 - 16?
• (-4)2 - 16 = 0 True
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x = -4 and x = 4
Teacher Reflections
»» Ask a student to write
the expression and its
factors on the board
explaining his/her
reasoning.
KEY: » next step
»» Can students get
the factors of »
x2 - b2 = 0
and hence solve
equations of the
form »
x2 - b2 = 0?
15
Teaching & Learning Plan: Quadratic Equations
Teacher Input
Student Activities: Possible
Responses
Teacher’s Support and
Actions
Assessing the Learning
»» How can you use the
following diagrams of two
squares to graphically show
that x2 - y2 = (x + y) (x - y)?
• Area of the small square is y2
and the area of the big square
is x2.
»» Draw the squares on the
board.
»» Can students see
how this is a physical
representation of »
x2 - y2 = (x + y) (x - y)?
• Area of the unshaded region is
x2 - y2.
y
2
x2
• The area of the unshaded
region is also x(x - y) + y(x - y).
x-y
y2
x
Teacher Reflections
x-y
y2 y
y
• Hence x2 - y2 = x(x - y) + y(x - y).
• Hence x2 - y2 = (x + y) (x - y)?
»» Complete Section E: Student
Activity 5.
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»» Distribute Section E: Student »» If students are
Activity 5.
having difficulties,
allow them to
»» Circulate the room and
talk through their
work.This will help
them identify their
misunderstandings
and misconceptions.
Difficulties identified
can then be
KEY: » next step
16
Teaching & Learning Plan: Quadratic Equations
Student Activities:
Possible Responses
Teacher’s Support and Actions
Assessing the
Learning
Section F: To solve quadratic equations using the formula
(Higher Level only)
»» Is x2 + 3x + 1 a quadratic equation?
»
»» Can you find the factors of»
x2 + 3x + 1?
• Yes, because the
highest power of the
unknown is 2.»
• No
»» Mathematicians use the formula »
»
2
»
to find the solutions to quadratic equations
when they are unable to find factors. It is
worth noting however that the formula
can be used with all quadratic equation.»
»» We will now try it for »
x2 + 3x + 2 = 0, which we already know has
x = - 2 and x= - 1 as its solutions.
»» Give students time to consider
if they can get the factors and
»» Do students
see that
not all
are
factorable?
»» Write x2 + 3x + 1 = 0 on the
board.»
»» It is not always possible to solve quadratic
equations through the use of factors, but
there are alternative methods to solve
them.»
»» Comparing x2 + 3x + 1 = 0 to the general
form of a quadratic equation »
ax2 + bx + c = 0.
What are the values of a, b and c?
»» Write the expression on the
board.»
Teacher Reflections
»» Write a = 1, b = 3 and c = 1 on
the board.
•
a = 1, b = 3 and c = 1
»» Write x2 + 3x + 2 = 0 and
(x + 2) (x + 1) = 0
x = -2 and x = -1 on the board.
»» Can students
complete
the formula?
»» Write the formula on the board.»
»
»
»
»
x = -1 or x = -2
© Project Maths Development Team 2011
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KEY: » next step
17
Teaching & Learning Plan: Quadratic Equations
Input
»» Solve x2 + 3x + 1 = 0 using the
formula.
Student Activities:
Possible Responses
• x = -2.816 and x = 0.382
Teacher’s Support and Actions Assessing the
Learning
»» Challenge students to find
the factors on their own
before going through the
algorithm.»
Teacher Reflections
»» Write on the board»
»
»
»
»
x = -2.618 or x = -0.382
»» Complete the exercises in Section F:
Student Activity 6.
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»» Distribute Section F: Student
Activity 6.
KEY: » next step
»» Can students use
the formula to
equations?
18
Teaching & Learning Plan: Quadratic Equations
Student Activities: Possible
Responses
Teacher’s Support and Assessing the Learning
Actions
Section G: To solve quadratic equations given in rational form
• 3x2 - 2x = 0
x (3x - 2) = 0
x = 0 or x = 2/3
»» Simplify »
»
»
»» Get individual
students to write
the solution on the
board and explain
their work.
»» Can students convert
equations given in
simple fraction form
to the form»
ax2 + bx + c = 0?
»» Get an individual
student to write
the solution on the
board and explain
their reasoning.
»» Can students simplify
the equation and
then solve it?
»» Now solve the equation.
»» Write x + 3 = 10/x in the form
ax2 + bx + c = 0
x + 3 = 10/x
x2 + 3x -10 = 0
• Multiplied both sides by x.
»» How did you do this?»
»» Hence solve x + 3 = 10/x
• (x + 5) (x - 2) = 0
x = -5 or x = 2
(-5) 2 + 3 (-5) -10 = 0 True»
(2) 2 + 3 (2) -10 = 0 True
»» Attempt the questions on Section G:
Student Activity 7.
© Project Maths Development Team 2011
•
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Teacher Reflections
»» Distribute Section G: »» Can students correctly
Student Activity 7.
on the activity sheet?
»» Circulate the room
misconceptions.
KEY: » next step
19
Teaching & Learning Plan: Quadratic Equations
Student Activities: Possible Teacher’s Support and Assessing the
Responses
Actions
Learning
Section H: To form quadratics given whole number roots
(Higher Level Only)
»» What are the factors of x2 + 6x + 8?
• (x + 4) (x + 2)
»» What is the solution of x2 + 6x + 8 = 0?
•
»» If we were told the equation had roots »
x = -4 and x = -2, how could we get an
equation?
»» Given that an equation has roots 2 and 5, write
the equation in the form (x - s) (x - t) = 0.
»» Then write it in the form ax2 + bx + c = 0.
x = -4 and x = -2
• (x - (-4)) (x- (-2)) = 0
(x + 4) (x + 2) = 0
x2 + 4x + 2x + 8 = 0
x2 + 6x + 8 = 0
• (x -2) (x -5) = 0
»
»
x2 -2x -5x + 10 = 0
x2 -7x + 10 = 0
»» Given that an equation has roots 1 and -3, write • (x -1) (x + 3) = 0
the equation in the form ax2 + bx + c = 0.
x2 - 1x + 3x - 3 = 0
x2 + 2x -3 = 0
»» Challenge the
students to find
the equation for
themselves.»
»» Get individual
students to write
the solution on the
board and explain
their work.
»» Write students’
responses on the
board.
»» Given the roots,
can students
write the
equation in the
form »
ax2 + bx + c = 0?
•
»» What do you notice about the following
equations:»
x2 + 2x - 8 = 0
2x2 + 4x - 16 = 0
8 - 2x - x2 = 0?
»» Now complete Section H: Student Activity 8.
© Project Maths Development Team 2011
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• They are the same
equations but are
arranged in a different
order.
Teacher Reflections
»» Write students’
responses on the
board.
»» Write each equation »» Can students
on the board.
recognise that
the equations
are the same?
»» Distribute Section H:
Student Activity 8.
KEY: » next step
20
Teaching & Learning Plan: Quadratic Equations
Section A: Student Activity 1
Note:It is always good practice to check solutions. The roots of a quadratic
equation are the elements of its solution set. For example if x = 1, x = 2
are the root ⇒ {1, 2} = solution set. The roots of a quadratic equation are
another name for its solution set.
1. If xy = 0, what value must either x or y or both have?
2. Write in your own words what solving an equation means.
3. Solve the following equations:
a. (x - 1) (x - 2) = 0
b. (x - 4) (x - 5) = 0
c. (x - 3) (x - 5) = 0
d. (x - 2) (x - 5) = 0
4. What values of x make the following statements true:
a. (x - 2) (x - 5) = 0 b. (x - 4) (x + 5) = 0
c. (x - 2) (x + 4) = 0
5. Find the roots of (x - 4) (x + 5) = 0.
6. Solve the equation (x - 3) (x + 2) = 0.
Hence state what the roots of (x - 3) (x + 2) = 0 are.
7. Find a positive value for x that makes the statement (x - 4) (x + 2) = 0
true.
8. Solve the following equations:
a. x (x - 1) = 0
b. x (x - 2) = 0
c. x (x + 4) = 0
9. a. These students each made at least one error, explain the error(s) in
each case:
Student C
Student B
Student A
(x - 8) (x - 9) = 0
(x - 7) (x - 9) = 0
(x + 5) (x + 9) = 0
x-8=0
x-9=0
x-7=0
x-9=0
x+5=0
x+9=0
x = -8
x=9
x = -7
x = -9
x=5
x=9
b. Solve each equation correctly showing all the steps clearly.
10.If x = 5 is a solution to the equation (x - 4) (x - b) = 0,
what is the value of b?
11.Is x = 3 a solution to the equation (x - 3) (x - 2) = 2.
Explain your reasoning. Solve this equation.
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21
Teaching & Learning Plan: Quadratic Equations
Section B: Student Activity 2 (continued)
1. a. Compete the following table:
x
−4
−3
−2
−1
0
1
2
x+2
x+1
y = f (x) = (x + 2) (x + 1)
b. From the table above determine the values of x for which the equation
is equal to 0.
c. Solve the equation (x + 2) (x + 1) = 0 by algebra.
d. What do you notice about the answer you got to parts b. and c. in this
question?
e. Draw a graph of the data represented in the above table.
f. Where does the graph cut the x axis? What is the value of
f (x) = (x + 2)(x + 1) at the points where the graph cuts the x axis?
g. Can you describe three methods of finding the solution to
(x + 2) (x + 1) = 0.
2. Solve the equation (x - 1) (x - 4) = 0 a) by table, b) by graph and c)
algebraically.
3. Write the equation represented in this table in the form (x−a)(x−b)=0.
x
−2
−1
0
1
2
3
© Project Maths Development Team 2011
f(x)
20
12
6
2
0
0
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22
Teaching & Learning Plan: Quadratic Equations
Section B: Student Activity 2
4. The graph of a quadratic function f (x) = ax2 + bx + c is represented by the
curve in the diagram below. Find the roots of the equation f (x) = 0 and
so identify the function.
5. The graph of a quadratic function f (x) = ax2 + bx + c is represented by the
curve in the diagram below. Find the roots of the equation f (x) = 0 and
so identify the function.
6. Where will the graphs of the following functions cut the x axis?
a. f (x) = (x - 7) (x - 8)
b. f (x) = (x + 7) (x + 8)
c. f (x) = (x - 7) (x + 8)
d. f (x) = (x + 7) (x - 8)
7. For what values of x does (x - 7) (x - 8) = 0?
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23
Teaching & Learning Plan: Quadratic Equations
Section C: Student Activity 3
Note: It is always good practice to check solutions.
It is recommended you use the Guide number method to find the factors.
1. Solve the following equations:
a. x2 + 6x + 8 = 0
b. x2 + 5x + 4 = 0
c. x2 - 9x + 8 = 0
d. x2 - 6x + 8 = 0
2. Solve the equations:
a. x2 + 2x = 3
b. x (x - 1) = 0
c. x (x - 1) = 6
3. Are the following two equations different x (x - 1) = 0 and x (x - 1) = 6? Explain.
4. When a particular Natural number is added to its square the result is 12. Write
an equation to represent this and solve the equation. Are both solutions
realistic? Explain.
5. A number is 3 greater than another number. The product of the numbers is 28.
Write an equation to represent this and hence find two sets of numbers that
satisfy this problem.
6. The area of a garden is 50cm2. The width of the garden is 5cm less than
the breadth. Represent this as an equation. Solve the equation. Use this
information to find the dimensions of the garden.
7. A garden with an area of 99m2 has length xm. Its width is 2m longer than its
length. Write its area in term of x. Solve the equation to find the length and
width of the garden.
8. The product of two consecutive positive numbers is 110. Represent this as an
algebraic equation and solve the equation to find the numbers.
9. Use Pythagoras theorem to generate an equation to represent the information
in the diagram below. Solve this equation to find x.
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24
Teaching & Learning Plan: Quadratic Equations
Section C: Student Activity 3 (continued)
10.One number is 2 greater than another number. When these two
numbers are multiplied together the result is 99. Represent this problem
as an equation and solve the equation.
11.Examine these students’ work and spot the error(s) in each case and
solve the equation fully:
Student A
Student B
Student C
x2 - 6x - 7 = 0
(x + 7)
(x + 1) = 0
x = -7
x = -1
x2 - 6x - 7 = 0
(x - 7)
(x + 1) = 0
x=7
x=1
x2 - 6x - 7 = 0
(x - 1)
(x + 7) = 0
x=1
x = -7
12. a. Complete a table for x2 - 2x + 1 for integer values between -2 and 2.
b. Draw the graph of x2 - 2x + 1 for values of x between -2 and 2.
Where does this graph cut the x axis?
c. Factorise x2 - 2x + 1 and solve x2 - 2x + 1 = 0.
d. What do you notice about the values you got for parts a), b) and c)?
13. a. Complete a table for x2 + 3x + 2 for integer values between -3 and 3.
b. Draw the graph of x2+3x+2 for values of x between -3 and 3. Where
does this graph cut the x axis?
c. Factorise x2+3x +2 and solve x2+3x +2=0.
d. What do you notice about the values you got for parts a), b) and c)?
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25
Teaching & Learning Plan: Quadratic Equations
Section D: Student Activity 4
Note: It is always good practice to check solutions.
It is recommended you use the Guide number method to find the factors.
1. Find the factors of 2x2 + 7x + 3. Hence solve 2x2 + 7x + 3 = 0.
2. Find the factors of 3x2 + 4x + 1. Hence solve 3x2 + 4x + 1 = 0.
3. Find the factors of 4x2 + 4x + 1. Hence solve 4x2 + 4x + 1 = 0.
4. Find the factors of 3x2 - 4x + 1. Hence solve 3x2 - 4x + 1 = 0.
5. Find the factors of 2x2 + x - 3. Hence solve 2x2 + x - 3 = 0.
6. a. Is 2x2 + x = 0 a quadratic equation? Explain your reasoning.
b. Find the factors of 2x2 + x. Hence solve 2x2 + x = 0.
7. Factorise 4x2 - 1x2 + 9. Hence solve 4x2 - 1x2 + 9 = 0.
8. Twice a certain number plus four times the same number less one is 0.
Find the numbers.
9. a. Complete the following table and using your results, suggest
solutions to 2x2 + 3x + 1 = 0.
x
2x2
3x
1
-2
1
-1
1
0
1
1
1
2
1
2x2 + 3x + 1
b. Using the information in the table above, draw a graph of
f(x) = 2x2 + 3x + 1, hence solve the equation.
c. Did your results for a. agree with your results in b?
10.Find the function represented by the curve in the
diagram opposite in the form f (x) = ax2 + bx + c = 0.
Then solve the equation.
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26
Teaching & Learning Plan: Quadratic Equations
Section E: Student Activity 5
1. Factorise:
a. x2 - 25
b. x2 - 49
2. Solve:
a. x2 - 36 = 0
b. 36 - x2 = 0
c. n2 - 625 = 0
d. x2 - x = 0
e. 3x2 - 4x = 0
f. 3x2 = 11x
g. (a + 3)2 - 25 = 0
3. Think of a number, square it, and subtract 64. If the answer is 0, find the
number(s).
4. Given an equation of the form x2 - b = 0, write the solutions to this
equation in terms of b.
5. Solve the equation x2 - 16 = 0 graphically. Did you get the results you
6. Calculate:
a. 992 - 1012
b. 1032 - 972
Higher Level Only
7. Solve the following equations:
a. 4x2 - 36 = 0
b. 4x2 - 9 = 0
c. 4x2 - 25 = 0
d. 16x2 - 9 = 0
8. A man has a square garden of side 20m. He builds a pen for his dog in
one corner. If the area of the remaining part of his garden is 144m2, find
the dimensions of the dog’s pen.
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27
Teaching & Learning Plan: Quadratic Equations
Section F: Student Activity 6
1. Using the formula solve the following equations:
a. x2 + 5x + 4 = 0
b. x2 + 4x + 3 = 0
c. x2 + 4x -3 = 0
d. x2 - 4x + 3 = 0
e. x2 - 4x -3 = 0
f. x2 - 4 = 0
g. x2 + 3x = 4
h. x2 + 2x -3 = 0
2. Solve the equation x2 -5x - 2 = 0. Write the roots in the form a±√b.
3. Given 2+√3 as a solution to the equation ax2 + bx + c = 0 find the other
solution.
4. When using the quadratic formula to solve an equation and you know
x = 3 is a solution, does that mean that x = -3 is definitely the other
solution? Explain your reasoning with examples.
5.
a. Solve the equation x2 + x2 + 1 = 0 by using a:
i. Table.
ii.Graph.
iii.Factors.
iv.Formula.
b. Did you get the same solutions using all four methods?
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28
Teaching & Learning Plan: Quadratic Equations
Section G: Student Activity 7
Solve the following equations:
2. Square a number add 9, divide the result by 5. The result is equal to
twice the number. Write an equation to represent this and solve the
equation.
3. A prize is divided equally among five people.
If the same prize money is divided among six people each prize winner
would get €2 less than previously. Write an equation to represent this
and solve the equation.
© Project Maths Development Team 2011
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29
Teaching & Learning Plan: Quadratic Equations
Section G: Student Activity 7
Higher Level Only
1. If the roots of the following quadratic equations are as follows write
the equations in the form (x - s) (x - t) = 0:
a. 2 and 3
b. 2 and -3
c. -2 and -3
d. -2 and 3
e. 2 and ¾
2. What is the relationship between the roots of a quadratic equation and
where the graph of the same quadratic cuts the x axis?
3. The area of the triangle below is 8cm2. Find the length of the base and
the height of the triangle.
4. A field is in the shape of a square with side equal to x metres. One side
of the field is shortened by 5 metres and the other side is lengthened
by 6 metres. If it is known the area of the new field is 126m2, write an
equation that represents the area of the new field. Solve the equation
and find the dimensions of the original square field.
5. a. Draw the graph of f (x) = 3x2 - 10x + 8 for values between -3 and 3.
Where does this graph cut the x axis?
b. Factorise and solve 3x2 - 10x + 8 = 0
c. What do you notice about the values you got for part a and part b?
6. Find the factors of 2x2 - 5x +3. Hence solve 2x2 - 5x + 3 = 0
© Project Maths Development Team 2011
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30
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