find the exact value of cos2a

Question

tan a=-3/2 and a is in quadrant iv

Answer 1

Step 1:

The trigonometric expression is .

Here, in the fourth quadrant.

Rewrite the trigonometric equation is

Double angle formula for trigonometric: .

Substitute in the above formula.

Half angle formula for trigonometric: .

Solution:

The value of .

Answer 2

Quadrant information is redundant

 

as  cos2A=(1-tan²A)/(1+tan²A)