Question

How do you evaluate `arc cos (-1/sqrt2)`?

Answer 1

`(3pi)/4; (5pi)/4`

Explanation:

Use trig table of special arcs and unit circle.
`cos x = - 1/sqrt2 = - sqrt2/2` -->
arc `x = +- (3pi)/4`
The arc `x = - (3pi)/4` is co-terminal to `x = (5pi)/4`
There for, the answers for `(0, 2pi)` are:
`(3pi)/4; (5pi)/4`