Question

For $a<0$, $\text{arg}\left(ia\right)$ is

• A. $\frac{\pi }{4}$
• B. $\frac{\pi }{2}$
• C. $\pi$
• D. $-\frac{\pi }{2}$

Answer 1

The correct option is D $-\frac{\pi }{2}$

For $z=ia,a<0$
$z$ must lies on negative imaginary axis.
Hence, $\arg \left(z\right)=\arg \left(ia\right)=-\frac{\pi }{2}$