Answer
$-3$
Work Step by Step
Need to solve $\cos 90^{\circ} +3 \sin 270^{\circ}$
Therefore, $\cos 90^{\circ} +3 \sin 270^{\circ} = \cos 90^{\circ} +3 \sin (90^{\circ}+ 180^{\circ}) \\= \cos 90^{\circ} +3 [-\sin 90^{\circ}] \\= 0+(3)(-1) \\=-3$
