Question

How do you simplify `cos(2sin^-1(4/5))`?

Answer 1

`-7/25`

Explanation:

Let `a = sin^(-1)(4/5).`

Then `sin a = 4/5`.

The given expression is

`cos 2a`

`= 1-2 sin^2a`

`=1-2(16/25)`

`=-7/25`.,