Answer
$10 i$
Work Step by Step
The given complex number can be written in the rectangular form as follows: $r (\cos \theta +i \sin \theta) = a+i b$
Where, $a=r \cos \theta ; b =r \sin \theta $
We are given that $r=10 $ and $\theta= 90^{\circ}$
Therefore, $10 (\cos 90^{\circ} +i \sin 90^{\circ}) = 10(0+1 i) \\ = 10 i$
