Lesson 4

1. Lesson 4

Mathematics 20-2 M1 Lesson 4

Module 1: Trigonometry

Lesson 4: Working with Multiple Oblique Triangles

Focus

This is a photo showing a kite in the sky.

iStockphoto/Thinkstock

This picture shows Jahnavi, Joey, and the kite. A right triangle has one side perpendicular to the ground, another side parallel to the ground, and the hypotenuse going from Jahnavi to the kite. The angle of elevation at Jahnavi is 37 degrees. A second right triangle has one side perpendicular to the ground, another side parallel to the ground, and the hypotenuse goes from Joey to the kite. The angle of elevation at Joey is 62 degrees. The distance between Jahnavi and Joey is 90 m.

Joey is flying a kite and wants to determine its height. He enlists the help of his friend, Jahnavi, who is standing 90 m away. Joey uses a clinometer and determines that the angle of elevation to the kite is 62°. Jahnavi determines that the angle of elevation is 37°.

There are multiple triangles in this diagram, and one of them is oblique. Should you use the primary trigonometric ratios? Should you use the sine law or the cosine law?

In Lesson 1 you solved problems involving multiple right triangles. In the last two lessons you learned how to solve problems involving oblique triangles. In this lesson you will combine these skills to help you decide whether the primary trigonometric ratios, sine law or cosine law, should be used to solve problems involving multiple oblique triangles. Solving problems involving multiple oblique triangles is at the heart of triangulation, which you will do in the Module 1 Project.

This lesson will help you answer the following inquiry question:

How do you determine when to use the sine law and when to use the cosine law?

Assessment

Lesson 4 Assignment
Module 1 Project

All assessment items you encounter need to be placed in your course folder.

Save a copy of the Lesson 4 Assignment to your course folder. You will receive more information about how to complete the assignment later in this lesson.