Question

What is cos ^ -1 ( cos (7 pi/4) )?

Answer 1

`(7pi)/4`

Explanation:

`cos` and `cos^-1` are effectively just opposite functions of each other. In other words, if `cos(theta) = x` then `cos^-1(x) = theta`. That means if you take the `cos^-1` of a `cos(theta)` statement, you just get the original `theta` value back.

`cos^-1(cos(theta))=cos^-1(x) = theta`

So the given problem simplifies down to `(7pi)/4`, the original `theta` value.