Calculus Question

Question

Express the following as a function of twice the given angle: cos x = 4/5

1. 16/25

2. 7/25

3. 3/5

4. 5/4

Answer 1

cosx=4/5

cos2x=2cos^2x-1

2cos^2x-1=

2(4/5)^2-1=

2(16/25)-1=

(32/25)-1=

1 7/25 - 1=

7/25 which is 2.