Teaching & Learning Plans Plan 8: Introduction to Trigonometry 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 teacher input and gives details of the key student tasks and teacher questions which move the lesson forward. ii. Student Activities – Possible and Expected 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. Checking Understanding: 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 8: Introduction to Trigonometry Aims • To introduce the concept of trigonometry • To understand the concept of sin, cos and tan • To apply trigonometry to solve problems Prior Knowledge Students should have knowledge of the concept of ratio and should know that division is not commutative. Students should be able to use a calculator to convert fractions, correct to three decimal places, measure the lengths of sides of a triangle to the nearest millimetre and draw to scale. Students should have studied Pythagoras’ Theorem and know the meaning of the term “hypotenuse”. Students may have studied similar triangles in geometry – the fact that corresponding sides are proportional makes trigonometry possible. Students will have understood how to calculate mean. Students should know how to use a measuring tape and protractor. Learning Outcomes As a result of studying this topic, students will be able to • correctly identify the hypotenuse in a right angled triangle, and the opposite and adjacent sides of a given angle • find a pattern linking the ratio of sides of a triangle with the angles and hence understand the concepts of sine, cosine and tangent ratios of angles • apply trigonometry to solve problems including those involving angles of elevation and depression © Project Maths Development Team 2009 www.projectmaths.ie 1 Teaching & Learning Plan 8: Introduction to Trigonometry Relationship to Junior Certificate Syllabus Sub-topics Ordinary Level Higher Level (also includes OL) Trigonometry Solution of right-angled triangle problems of a simple nature involving heights and distances, including the use of the theorem of Pythagoras. Functions of 30˚, 45˚ and 60˚ in surd form derived from suitable triangles. Cosine, sine and tangent of angles (integer values) between 0˚ and 90˚. Decimal and DMS values of angles. Solution of right-angled triangles. Resources Required Calculators, measuring tapes, graph paper, cm rulers and a sunny day! Introducing the Topic Trigonometry is simply geometrical constructions where the ratio of the side lengths in triangles is used to determine angular measurement. Trigon, meaning triangle and metria, meaning measurement Mathematicians have used trigonometry for centuries to accurately determine distances without having to physically measure them (Clinometer Activity Appendix A). It can also be used to calculate angles that would be very difficult to measure. Trigonometry has uses in such areas as surveying, navigation, drawing and architecture. © Project Maths Development Team 2009 www.projectmaths.ie 2 »» Students measure one student’s height and the length of his/her shadow and fill in Student Activity 1A. Outside Classroom »» We are going to find the angle of elevation of the sun. Fill in Student Activity 1A. © Project Maths Development Team 2009 www.projectmaths.ie »» Students fill in Student Activity 1D to find the measure of some tall object and check their answer with other students in the class. »» Now using the angle of elevation (from Student Activity 1C) and the length of the shadow of an object whose height you cannot physically measure (from Student Activity 1B), again use a scaled diagram to determine the height of the object. »» From your scaled diagram work out the angle of elevation of the sun. »» Students fill in Student Activity 1C to find the angle of elevation of the sun and check their answer with other students in the class. Inside Classroom »» Fill in Student Activity 1C. »» Students measure the length of the shadow of some tall object e.g. flagpole or goalpost and fill in Student Activity 1B. Student Activities: Possible and Expected Responses Student Learning Tasks: Teacher Input KEY: » next step • student answer/response »» Can students identify the angle of elevation? »» Walk around observing students as they take measurements. »» Circulate checking that students can draw a scaled diagram. »» Have all students understood the task so far? Checking Understanding »» Distribute Student Activity 1 (sunny day necessary!) Teacher’s Support and Actions Lesson Interaction Teaching & Learning Plan 8: Introduction to Trigonometry 3 »» Students can mark the hypotenuse of each right angled triangle. »» Collaborate in pairs as you fill in Student Activity 2. © Project Maths Development Team 2009 www.projectmaths.ie »» Mark the hypotenuse on the triangles in Student Activity 2 of right-angled triangles. • The longest side • The side opposite the 90° angle »» What is the hypotenuse of a right-angled triangle? »» Why is the study of triangles important?– show students the PowerPoint images in Appendix B. Note: Later on, having learned about the trigonometric ratios of sin, cos and tan studentscan use these trigonometric ratios to determine the angle of elevation of the sun and hence the height of for example a tall tree or a goalpost. KEY: » next step »» Mark the hypotenuse on the board with an arrow to show that the side is opposite the right angle. »» Draw a large right angled triangle with the right angle marked. »» Have the heading “Right angled triangles” on the board. (RHS of the board should have heading “New Words”). »» Distribute Student Activity 2. • student answer/response »» Are all students able to identify the hypotenuse? »» Have all students been able to complete Student Activity 1E? »» Alternatively, you can use ratios in similar triangles. Fill in Student Activity 1E. »» Students complete Student Activity 1E. Checking Understanding Student Learning Tasks: Teacher Student Activities: Possible Teacher’s Support and Actions Input and Expected Responses Teaching & Learning Plan 8: Introduction to Trigonometry 4 • 90° • Complementary angles • The hypotenuse »» How many degrees do they add up to? »» What are these angles called? »» Mark either one of the two complementary angles on the triangle with an arc. What is the name of one of the arms of that angle? © Project Maths Development Team 2009 www.projectmaths.ie »» The other side, which is beside »» Students mark one angle with an arc and label the marked angle, is given the name “adjacent”. Label it. the adjacent side to this angle on all the triangles. • Two »» How many other angles are in the triangle? KEY: » next step »» Circulate checking that students can label the sides correctly; emphasising that the labelling of a side depends on the angle it refers to. Adjacent means adjacent to a particular angle. »» Point out on the board that regardless of which of the two angles adding up to 90° is chosen by the student, the hypotenuse is one of the arms of that angle. »» Tell students that the word adjacent means “beside”. They are sitting beside or “adjacent to” another student. »» Label the adjacent and write the word “Adjacent” in the new words list on RHS of board. »» Label the hypotenuse on the triangle on the board. Student Activities: Possible Teacher’s Support and Actions and Expected Responses Student Learning Tasks: Teacher Input Teaching & Learning Plan 8: Introduction to Trigonometry • student answer/response »» Can all students identify the side adjacent to the marked angle? Checking Understanding 5 »» If a student cannot explain the answer, give two lengths and then ask the student if the order matters. »» Divide the length of one side by the length of another side using the same units. »» Yes, because 3/2 is not the same as 2/3 for instance. »» If you were to work out the ratio of any two of the sides in a right angled triangle how would you do this? © Project Maths Development Team 2009 www.projectmaths.ie »» Are students familiar with the concept of ratio and do they understand that division is not commutative? »» Ask students to think about the answer first and then ask a student for an answer. »» Students label 90° angle, the hypotenuse, one other angle then adjacent and then opposite sides. »» Repeat this process of marking angles and labelling sides for all the triangles on Student Activity 1. »» Would the order matter? Explain your answer. »» Are all sides correctly labelled in each triangle? »» Circulate checking the work of each group. • If you were standing at the vertex of the marked angle it would be across from you or opposite you so it is called the opposite side. »» Describe the opposite side. KEY: » next step • student answer/response »» Check each group’s work as »» Are all sides correctly they are labelling the sides labelled in each triangle? of the triangle. »» Students label the side opposite the marked angle as the opposite. Checking Understanding »» Label the third side of the triangle as the opposite side. Teacher’s Support and Actions Student Activities: Possible and Expected Responses Student Learning Tasks: Teacher Input Teaching & Learning Plan 8: Introduction to Trigonometry 6 © Project Maths Development Team 2009 »» Students work on Student Activities 3, 4, 5, 6, 7 and 8. www.projectmaths.ie »» One student is to measure, one to calculate ratios and one to double check changing roles on each triangle. »» Student Activities 3, 4, 5, 6, 7 and 8: For each triangle of the five triangles mark the 90° angle and one other given angle (given on the sheet). Label the sides of the right angled triangles as hyp (hypotenuse), adj (adjacent), and opp (opposite). Measure each side correct to the nearest mm and calculate the ratios opp/hyp, adj/hyp, opp/adj. • One is the inverse of the other. If they were multiplied, they would »» If I knew the answer to the first give an answer of 1. ratio was ½, what would be the answer to the second one? • 2/1 »» What is the relationship between the first pair? »» When giving the ratios use the names for the sides. »» How many possible ratios could • 6 be worked out for a rightangled triangle? • student answer/response »» Are students measuring accurately and calculating ratios correctly i.e. opp/hyp and not hyp/opp? KEY: » next step »» Emphasise that students should measure accurately to the nearest mm. »» Distribute Student Activity 3, 4, 5, 6 ,7 and 8 to different groups of 3-4 students each i.e. one Student Activity per group. »» Circle and tell students that you will concentrate on these 3 as the others are their multiplicative inverses. »» Do students know the concept of a multiplicative inverse? »» Write the ratios on the board »» Are the students able as students call them out to take the 3 sides and placing multiplicative inverses combine them into 6 beside each other. pairs? Student Learning Tasks: Teacher Student Activities: Possible Teacher’s Support and Actions Checking Understanding Input and Expected Responses Teaching & Learning Plan 8: Introduction to Trigonometry 7 © Project Maths Development Team 2009 • »» If so, which one or which ones and why? - The opposite is www.projectmaths.ie bigger than the adjacent when it is opposite the bigger of the 2 complimentary angles. • Yes • Numerator will always be smaller than the denominator as the hypotenuse is the longest side. • »» Is it possible for any of the ratios to be bigger than 1? »» Explain. »» Of the 3 ratios which of them can never be bigger than 1? ? • student answer/response »» Do students understand that the only one of the three ratios which can be bigger than 1 is »» Have they been able to answer this question based on their knowledge of right angled triangles? »» Are the students finding that the ratios are unchanged for a particular angle regardless of the size of the triangle? Checking Understanding KEY: » next step »» If students cannot answer this question, give an example using numbers when fractions give answers greater than 1 or less than 1. »» Circulate checking the progress of the different groups to see that sides are being labelled correctly and that students understand the task. »» Ask the class when they have a few of the ratios calculated to answer this question and then ask one group to explain. • The ratios are unchanged »» If a group has difficulty for a particular angle seeing the pattern or regardless of the size of the verbalising it you will see triangle. this as you circulate and help by using leading questions. »» Write down what you have observed from your answers. Teacher’s Support and Actions Student Activities: Possible and Expected Responses Student Learning Tasks: Teacher Input Teaching & Learning Plan 8: Introduction to Trigonometry 8 © Project Maths Development Team 2009 »» Each group gives the answers for each ratio for the angle they have worked on. www.projectmaths.ie »» On the master table, Student Activity 9 fill in the mean value you have calculated for sin, cos and tan of the angle from your own Student Activity 3, 4, 5, 6, 7, or 8. Tell the rest of the class the values you have calculated. • student answer/response »» Have all students understood the tasks so far, completed them for all the triangles, and filled out the master table? Checking Understanding KEY: » next step »» Draw a master table on the board and fill in the answers as they are given telling students that they will be able to check those answers in the next step. »» Hand out Student Activity 9. »» Go back to Student »» Beside each ratio students »» Tell students that sin is the Activities 3 - 8 and fill in fill in the appropriate name short version of sine, cos is the name of each ratio, for plus the angle it refers to. short for cosine and that tan example for the sheet with is the shortened version of the angles of 30° fill in opp/hyp word ‘tangent’. = sin 30° etc. »» Students write this heading »» Write the word and the ratios into their TRIGONOMETRY on the board. copies. »» Tell the students that the ratios they have investigated have special names and write them on the board. »» »» We have been studying how the sides and angles of triangles are related to each other. This is called TRIGONOMETRY – Trigon meaning triangle and metria meaning measurement. Teacher’s Support and Actions Student Activities: Possible and Expected Responses Student Learning Tasks: Teacher Input Teaching & Learning Plan 8: Introduction to Trigonometry 9 © Project Maths Development Team 2009 »» Circulate to ensure that students are able to see the patterns and are using correct terminology. »» Distribute Student Activity 10. »» Circulate to see that the values of sin, cos and tan of angles calculated through measurements agree with those found on the calculator. »» Emphasise that sin, cos and tan are functions of angles. »» Show students how to check if their calculator is in degree mode and, if not, how to put it into this mode. Teacher’s Support and Actions KEY: » next step • Students may be familiar with »» Write on the board - Given a trig ratio, for example sin A the SHIFT or 2nd function = 0, the angle A = sin-1(0.5). button on the calculator and hence suggest using this Emphasise that sin-1x, cos-1 x button. and tan-1 x represent angles where x is a ratio of sides in a right angled triangle. www.projectmaths.ie »» If you knew the ratios how would you find out the angle? Given that the sin of an angle is 0.5 how do you find the angle? »» Using the answers on Student »» Students see patterns in the answers on the master table. Activity 9, answer the questions on Student Activity 10. »» Using the calculator check the values of sin, cos and tan of the angles, which you have calculated through measurement. Check the measurements of the rest of the class also. »» Students check the values in the master table with the values got using the calculator and fill in to “check” columns on the master table Student Activity 9. • Degrees »» What units are angles measured in? »» There are other units for measuring angles such as radians, which you will meet later on so you must be sure your calculator is in degree mode if you are using degrees. Student Activities: Possible and Expected Responses Student Learning Tasks: Teacher Input Teaching & Learning Plan 8: Introduction to Trigonometry • student answer/response Checking Understanding 10 • Trigonometry is about the study of the relationship between angles and ratio of sides in triangles. Reflection »» List what you have learned today. © Project Maths Development Team 2009 »» Write down any questions you may have. »» Write down anything you found difficult. »» Students use their calculators to evaluate these angles. »» Given www.projectmaths.ie • The three ratios of sides in a right angled triangle are: • The sides in a right angled triangle are labelled hypotenuse, and then adjacent and opposite depending on which of the two complementary angles is of interest. Student Activities: Possible and Expected Responses Student Learning Tasks: Teacher Input KEY: » next step »» Circulate and take note particularly of any questions students have and help them to answer them. Teacher’s Support and Actions Teaching & Learning Plan 8: Introduction to Trigonometry • student answer/response »» Are students using the terminology with understanding? Checking Understanding 11 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 1 Me and my shadow Safety warning: Never look directly at the sun Name: _________________________________________ Class: _____________________________ Date: _________________________________________ Time: ______________________________ When the sun is high, your shadow is short. When the sun is low, your shadow is long. Student Activity 1A • Show the angle of elevation of the sun on the above diagram. Call it A. • Describe the angle of elevation of the sun in terms of the two arms of the angle._________________________________________________________________________________________ _______________________________________________________________________________________________ _______________________________________________________________________________________________ • Measure the height of one of the students in your group and the length of their shadow. • Height of the student: __________cm. Length of the shadow _____________________cm. • Draw a rough sketch of a right-angled triangle to model the situation and write in the measurements. Student Activity 1B Measure the length of the shadow of some tall object e.g. flagpole or goalpost. Length of the shadow of a tall object which you cannot physically measure e.g. goalpost ______________________________cm © Project Maths Development Team 2009 www.projectmaths.ie 12 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 1C Back in class – Measuring the angle of elevation of the sun • Decide what scale to use. • Draw an accurate diagram on graph paper. Diagram 1 • Measure the angle of elevation of the sun from Diagram 1 above using a protractor. • Angle of elevation of the sun at _________ (time) on _______ (date) was ________. • Check your answer with other students in the class. • If you were to measure the angle of elevation of the sun at 10 a. m and another class measured the angle at 11 a.m. what would be the difference in the measurements?_______________________________ © Project Maths Development Team 2009 www.projectmaths.ie 13 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 1D Knowing the angle of elevation of the sun, measure the height of a tall object using the length of its shadow as previously measured. • Decide what scale to use. Scale: ______________________ • Draw an accurate diagram on graph paper using the length of the shadow, the angle of elevation of the sun and forming right-angled triangle (ASA). Diagram 2 • Measure the height of the goalpost from Diagram 2 above and using the scale factor convert to its actual height. • Check the answer with other students in the class. Conclusion for part 2: The height of the goalpost is ___________________cm approximately. Would you expect the same answer if you took the measurements at different times of the day? Explain your answer.________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ © Project Maths Development Team 2009 www.projectmaths.ie 14 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 1E Using Similar Triangles • Using graph paper draw the above 2 diagrams overlapping, with the angles of elevation of the sun superimposed as shown by example in the diagram on the right. Label the diagram on the graph paper as in the diagram on the right. • What do you notice about the 2 vertical lines in the triangles? ______________________________________ _______________________________________________________________________________________________ • Measure the heights of the 2 vertical lines |ED| and |CB|. • Measure the 2 horizontal lines |AB| and |AD|. ____ _____ • What do you notice about the two ratios? ________________________________________________________ ________________________________________________________________________________________________ ________________________________________________________________________________________________ • Knowing |AB| and |CB| and the distance |AD| how could you find |ED| without knowing the angle of elevation |∠EAD| of the sun? © Project Maths Development Team 2009 www.projectmaths.ie 15 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 1E Ratios in Similar Triangles • Draw 3 different right angled triangles with the arms of the 90 degree angle being vertical and horizontal line segments, using the same angle of elevation which you calculated for the sun. Call the triangles T1, T2, T3. Measure the length of the vertical and horizontal line segments in these triangles. Vertical T1 Horizontal T1 Vertical T2 Horizontal T2 Vertical T3 Horizontal T3 What do you notice about the ratios of any 2 vertical line segments of any 2 of these triangles and the ratio of the corresponding horizontal line segments?_ ______________________________________________ _________________________________________________________________________________________________ _________________________________________________________________________________________________ _________________________________________________________________________________________________ © Project Maths Development Team 2009 www.projectmaths.ie 16 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 2 Labelling Sides in Right Angled Triangles © Project Maths Development Team 2009 www.projectmaths.ie 17 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 3 Calculating ratios for similar right angled triangles with angles of 30° • Measure and label the 90° and the 30° angles in the following triangles. What is the measure of the third angle? • Label the hypotenuse as “hyp”. With respect to the 30° angle, label the other sides as “adj” for adjacent and “opp” for • Complete the table below. Marked Angle Size=30° |opp|/mm |hyp|/mm |adj|/mm (for angle=30°) (for angle=30°) fraction decimal fraction decimal fraction decimal (for angle=30°) T1 T2 T3 T4 T5 Mean Value (correct to 2 decimal places) © Project Maths Development Team 2009 www.projectmaths.ie 18 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 4 Calculating ratios for similar right angled triangles with angles of 40° • Measure and label the 90° and the 40° angles in the following triangles. What is the measure of the third angle? • Label the hypotenuse as “hyp”. With respect to the 40° angle, label the other sides as “adj” for adjacent and “opp” for opposite. • Complete the table below. Marked Angle Size=40° |opp|/mm |hyp|/mm |adj|/mm (for angle=40°) (for angle=40°) fraction decimal fraction decimal fraction decimal (for angle=40°) T1 T2 T3 T4 T5 Mean Value (correct to 2 decimal places) © Project Maths Development Team 2009 www.projectmaths.ie 19 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 5 Calculating ratios for similar right angled triangles with angles of 45° • Measure and label the 90° and the 45° angles in the following triangles. What types of right angled triangle are these triangles?___________________________________________________________________ • Label the hypotenuse as “hyp”. With respect to the 45° angle, label the other sides as “adj” for adjacent and “opp” for opposite. • Complete the table below. Marked Angle Size=45° |opp|/mm |hyp|/mm |adj|/mm (for angle=45°) (for angle=45°) fraction decimal fraction decimal fraction decimal (for angle=45°) T1 T2 T3 T4 T5 Mean Value (correct to 2 decimal places) © Project Maths Development Team 2009 www.projectmaths.ie 20 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 6 Calculating ratios for similar right angled triangles with angles of 50° • Label the 90° and the 50° angles in the following triangles. What is the measure of the third angle? ______________________________________________________________________________________________ • Label the hypotenuse as “hyp”. With respect to the 50° angle, label the other sides as “adj” for adjacent and “opp” for opposite. • Complete the table below. Marked Angle Size=50° |opp|/mm |hyp|/mm |adj|/mm (for angle=50°) (for angle=50°) fraction decimal fraction decimal fraction decimal (for angle=50°) T1 T2 T3 T4 T5 Mean Value (correct to 2 decimal places) © Project Maths Development Team 2009 www.projectmaths.ie 21 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 7 Calculating ratios for similar right angled triangles with angles of 60° • Measure and label the 90° and the 60° angles in the following triangles. What is the measure of the third angle?__________________________________________________________________________________ • Label the hypotenuse as “hyp”. With respect to the 60° angle, label the other sides as “adj” for adjacent and “opp” for opposite. • Complete the table below. Marked Angle Size=60° |opp|/mm |hyp|/mm |adj|/mm (for angle=60°) (for angle=60°) fraction decimal fraction decimal fraction decimal (for angle=60°) T1 T2 T3 T4 T5 Mean Value (correct to 2 decimal places) © Project Maths Development Team 2009 www.projectmaths.ie 22 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 8 Calculating ratios for similar right angled triangles with angles of 70° • Measure and label the 90° and the 70° angles in the following triangles. What is the measure of the third angle?___________________________________________________________________________________ • Label the hypotenuse as “hyp”. With respect to the 70° angle, label the other sides as “adj” for adjacent and “opp” for opposite. • Complete the table below. Marked Angle Size=70° |opp|/mm |hyp|/mm |adj|/mm (for angle=70°) (for angle=70°) fraction decimal fraction decimal fraction decimal (for angle=70°) T1 T2 T3 T4 T5 Mean Value (correct to 2 decimal places) © Project Maths Development Team 2009 www.projectmaths.ie 23 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 9 Master table of class results for ratios of sides in right angled triangles Angle/° Check Check Check 30° 40° 45° 50° 60° 70° © Project Maths Development Team 2009 www.projectmaths.ie 24 Teaching & Learning Plan 8: Introduction to Trigonometry Student Activity 10 Using the master table of class results answer the following questions 1. What do you notice about sin 30° and cos 60°? _ __________________________________ ________________________________________________________________________________ 2.What do you notice about cos 30° and sin 60°?_ ___________________________________ ________________________________________________________________________________ 3.Can you explain what you have noticed using diagrams? 4.How would you describe angles 30° and 60°? _____________________________________ ________________________________________________________________________________ 5.Can you find similar examples in the master table? ________________________________ ________________________________________________________________________________ 6.For what angle in a right angled triangle is the opposite side one half of the hypotenuse? _ __________________________________________________________________ ________________________________________________________________________________ Draw a diagram to illustrate your answer. 7.For what angle in a right angled triangle are the opposite and adjacent sides equal? _ ________________________________________________________________________________ 8.Calculate for each angle A. Compare this to the value of Tan A. What do you notice? Can you justify the answer?_______________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ © Project Maths Development Team 2009 www.projectmaths.ie 25 Teaching & Learning Plan 8: Introduction to Trigonometry Appendix A Making and using a clinometer to find the height of a tall structure Materials required: Protractor, sellotape, drinking straw, needle and thread, paper clip. Drinking Straw Thread h1 A h2 Finding the height of a wall/spire/ flagpole using a clinometer Work in threes – one holding the clinometer, one reading the angle of elevation, one recording the angle of elevation. • Measure the height of the observer from eye to ground level. • Measure the distance from the observer to the base of the building (under the highest point). • Mark the position of the observer on the ground. © Project Maths Development Team 2009 www.projectmaths.ie • Hold the clinometer so that the string is vertical. • Now tilt the clinometer looking through the drinking straw so that the highest point on the top of the wall/flagpole/spire is visible. • Read the angle of elevation of this highest point to the nearest degree. • Draw a rough sketch of the situation marking in the distances measured and the angle of elevation. 26 Teaching & Learning Plan 8: Introduction to Trigonometry Appendix A Rough Sketch Height from ground to observer’s eye Distance from observer to the foot of the spire Angle of elevation to the top of the spire Back in class: • Calculate the height of a very tall object using a scaled diagram. • Using graph paper draw a scaled diagram of the above situation. Scale_______________ • Measure the height of the spire from the scaled diagram and using the scale factor convert to its actual height. • Height of the spire above the observer’s eye: ____________________ • Height from ground to the observer’s eye: ______________________ • Height of the spire: ___________________________________________ © Project Maths Development Team 2009 www.projectmaths.ie 27 Teaching & Learning Plan 8: Introduction to Trigonometry Appendix A Calculate the height of a very tall object using trigonometry Redraw the diagram (doesn’t have to be to scale) marking the right angle, the hypotenuse, the angle of elevation, the side adjacent to the angle of elevation and the side opposite the angle of elevation. Right angled triangle, sides labelled and measurements included • What side do you know the length of? _________________________________________ • What side do you require the length of? ________________________________________ • What trigonometric ratio in a right-angled triangle uses these 2 sides? ________________ Using trigonometry, calculate the height of the building. Angle of elevation of the top of the building Distance to the base of the building d Tan A = h1/d h1 Height of the observer h2 Height of the building h1+ h2 Question As you move towards or away from the building while sighting the top of the spire, the angle of elevation of the top of the spire varies. What angle of elevation would allow the height of the building to be measured by using the distance from the observer to the base of the building added to the observer’s height – i.e. no scaled drawing or trigonometry required? © Project Maths Development Team 2009 www.projectmaths.ie 28 Teaching & Learning Plan 8: Introduction to Trigonometry Appendix A Finding the height of a building with a moat around it h1 A B h2 d Work in threes – one holding the clinometer, one reading the angles of elevation, one recording the angles of elevation. • Measure the height of the observer from eye to ground level, h2, and fill into the table. h2 ⏐<A⏐ ⏐<B⏐ ⏐d⏐ h1 H = h1+h2 • Mark the position of the observer on the ground. • Hold the clinometer so that the string is vertical. • Now tilt the clinometers, looking through the drinking straw so that a point on the top of the wall/ flagpole/spire is visible. • Read the angle of elevation, <A, to the nearest degree and fill into the table. • The observer moves closer to the building and again views the top of the building through the drinking straw on the clinometer. • Read the angle of elevation, <B, to the nearest degree and fill into the table. • Measure the distance between the two viewing positions, d, of the observer and fill into the table below. • Draw a rough sketch of the situation marking in the distances measured and the angles of elevations. © Project Maths Development Team 2009 www.projectmaths.ie 29 Teaching & Learning Plan 8: Introduction to Trigonometry Appendix A Use a scaled diagram to calculate the height of the building with a moat Using graph paper draw a scaled diagram of the above situation. Scale _____________________ • Measure the height of the spire from the scaled diagram and using the scale factor convert to its actual height. • Height of the spire above the observer’s eye: _____________________ • Height from ground to the observer’s eye: _______________________ • Height of the spire: ______________________________________ © Project Maths Development Team 2009 www.projectmaths.ie 30 Teaching & Learning Plan 8: Introduction to Trigonometry Appendix A Calculating the height of a very tall object surrounded by a moat using trigonometry Redraw the diagram (which does not have to be to scale) labelling the sides and angles. Right angled triangle, sides labelled and measurements included • • • • • • • Fill in all the angle and side measurements known for triangles CBD and CAB. Fill in the other two angle measurements in triangle CAB. Of the two triangles CBD and CAB, which triangle do you have most information for? ______________ Which side do you require the length of in triangle CBD? _________________________________________ What side is shared by both triangles CAB and CBD? ______________________________________________ What rule can be used to calculate this side? _____________________________________________________ Calculations: • • • • • Label the sides in right angled triangle CBD appropriately as ‘hypotenuse’, ‘adjacent’ and ‘opposite’. Which side do you know the length of? _________________________________________________________ Which side do you require the length of ? _______________________________________________________ What trigonometric ratio in a right-angled triangle uses these 2 sides? _____________________________ Calculations to find the required length:_________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ • Complete the table below to find the height of the building H ⏐<A⏐ © Project Maths Development Team 2009 ⏐<B⏐ www.projectmaths.ie ⏐d⏐ h2 h1 H = h1+h2 31 Teaching & Learning Plan 8: Introduction to Trigonometry Appendix B © Project Maths Development Team 2009 www.projectmaths.ie 32

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