1. Geometry Lesson 8 – 4 Trigonometry Objective:
Find trigonometric ratios using right triangles.
Use trigonometric ratios to find angle measures in right triangles.

2. Trigonometry Comes from two Greek terms: trigon – meaning triangle
metron – meaning measure

3. Trigonometric Ratio
A ratio of the lengths of two sides of a right triangle.
One trig ratio of ABC is AC / AB
The triangles are similar by AA similarity.

4. Trig Ratios
Sine (written sin)
Opposite leg divided by hypotenuse

5. Trig Ratios
Cosine (written cos)
Adjacent leg divided by hypotenuse

6. Trig Ratios
Tangent (written tan)
Opposite leg divided by adjacent leg

7. Express each ratio as a fraction and as a decimal to the nearest hundredth.
sin P
tan P
cos Q
cos P
sin Q
tan Q

8. Express each ratio as a fraction and as a decimal to the nearest hundredth.
sin J
cos J
tan J
sin K
cos K
tan K

9. Use special right triangles to express the tangent of 30o as a fraction and as a decimal to the nearest hundredth.
Check on calculator:

10. Use special right triangles to express the cosine of 45o as a fraction and as a decimal to the nearest hundredth.
Check on calculator:

11. Real world
A certain part of a hiking trail slopes upward at about a 5o angle. After traveling a horizontal distance of 100 feet along this part of the trail, what would be the change in a hiker’s vertical position? What distance has the hiker traveled along the path?
(100)
(100)
Use you calculator to take 100 * (tan 5)
Be careful order matters how you plug it in on different calculators
(y)
(y)

12. Find x to the nearest hundredth.

13. Inverse Trig Ratios: Used to find Angles
Inverse sine
Inverse cosine
Inverse tangent

14. Inverse ratio What is tan 30? What is tan-1 0.58? Approximately 0.58
Use the inverse button (usually above the trig button, above tan)
Approximately 30o

15. Use a calculator to find the measure of angle A to the nearest tenth.

16. Use a calculator to find the measure of angle A to the nearest tenth.

17. Solve the right triangle (find all sides and angles)
Solve the right triangle (find all sides and angles). Round side measures to the nearest tenth and angle measures to the nearest degree.
Use tan instead of sin or
cos since 10.3 is rounded.

18. Solve the right triangle
Solve the right triangle. Round side measures to the nearest tenth and angle measures to the nearest degree.
FH = 12.0

19. Homework
Pg – 15 all, 16 – 44 EOE, 62, 66 – 86 EOE