Question

How do you find the exact value of `sin(-90)`?

Answer 1

`sin (-90) = -1`

Explanation:

`sin -90 = sin (360 - 90) = sin 270`

Angle `270^@` is third quadrant, where only tan and cot are positive.

Hence `sin 270 = sin (180 + 90) = - sin 90 = -1`