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

Mar 7, 2018

$\sin \left(- 90\right) = - 1$
$\sin - 90 = \sin \left(360 - 90\right) = \sin 270$
Angle ${270}^{\circ}$ is third quadrant, where only tan and cot are positive.
Hence $\sin 270 = \sin \left(180 + 90\right) = - \sin 90 = - 1$