Question

How do you find the exact value of `cos^-1(cos(pi/7))`?

Answer 1

`cos^(-1)(cos(pi/7))=pi/7`

Explanation:

As per definition of `cos^(-1)`, if `cosa=x`, `a=cos^(-1)x`

In the given problem, let `cos(pi/7)=v`

then as per definition `cos^(-1)v=pi/7` .................(1)

and putting value of `v=cos(pi/7)` in (1), we get

`cos^(-1)(cos(pi/7))=pi/7`