Question

Find the modulus and amplitude of the complex number $-5i$.

Answer 1

Given the complex number is $-5i$.

Now modulus of the complex number is $\sqrt{0^2+(-5{)}^2}=5$.

Since the point $-5i$ lies on the negative half of the imaginary axis. So the amplitude of the complex number is $-\frac{\pi }{2}$.