Question

Given
`sinx=-(15)/(17)` and cos x > 0, what is the exact solution of cos 2x?


`A. (161)/(289) B.(225)/(289) C.-(161)/(289) D.-(225)/(289)`

Answer 1

Recall that

cos(2x) = 1 - 2 sin²(x)

so given that sin(x) = -15/17, we have

cos(2x) = 1 - 2 (-15/17)² = -161/289