Answer
$\sin 225^{\circ}=-\frac{\sqrt 2}{2}$,
$\cos 225^{\circ}=-\frac{\sqrt 2}{2}$
$\tan 225^{\circ}=1$
Work Step by Step
Reference angle $\theta' =\theta-180^{\circ}$ if $\theta $ is in quadrant III.
$\implies \theta'=225^{\circ}-180^{\circ}=45^{\circ}$
Sine is negative, cosine is negative and tangent is positive in quadrant III.
$\implies \sin 225^{\circ}=-\sin 45^{\circ}=-\frac{\sqrt 2}{2}$,
$\cos 225^{\circ}=-\cos 45^{\circ}=-\frac{\sqrt 2}{2}$
and $\tan 225^{\circ}=\tan 45^{\circ}=1$
