Finding exact values for Cosine

Question

Let θ be an angle in quadrant III such that cos θ = −2/3

 

Find the exact values of all of the five other trigonometric functions.

Answer 1

For cos θ = -2/3 in QIII:

 

x = -2, y = -√5         this by Pythagoras

 

Use this to state other five functions.