Answer
$4i$
Work Step by Step
We know from the unit circle that:
$\cos \dfrac{\pi}{2}=0$ and $\sin \dfrac{\pi}{2}=1$
Thus,, we simplify the given expression as follows:
$4\left[\cos (\dfrac{\pi}{2})+i \ \sin (\dfrac{\pi}{2})\right]
\\=4 (0+1\cdot i)
\\= 4(0)+4(i)
\\ =4i$
