Answer:
-4i = 4(cos 270 +i sin 270)
Step-by-step explanation:
We have a+ib = r(cosθ+isinθ)
\(r=\sqrt{a^2+b^2}\texttt{ and }tan\theta =\frac{b}{a}\)
Here a = 0 and b = -4
Substituting
\(r=\sqrt{0^2+(-4)^2}\\\\r=4\\\\tan\theta =\frac{-4}{0}\\\\\theta =270^0\texttt{(Since a is zero and b is negative)}\)
-4i = 4(cos 270 +i sin 270)
