Answer
3 or 3+0i
Work Step by Step
We know that $\cos90^{\circ}=0$ and $\sin90^{\circ}=1$
Substituting these values in the expression and solving:
$3(\cos90^{\circ}+i\sin90^{\circ})=3(0+(1)i)=3(0)=3$
Therefore, the rectangular form is 3 or 3+0i.
