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4-1.Complex numbers
normal
Let $z$ be a purely imaginary number such that ${\mathop{\rm Im}\nolimits} (z) < 0$. Then $arg\,(z)$ is equal to
A
$\pi $
B
$\frac{\pi }{2}$
C
$0$
D
$ - \frac{\pi }{2}$
Solution
(d)Let $z = 0 + ib$, where $b < 0$. Then $z$ is represented by a point on $OY'$ (negative direction of $y – $axis), therefore $arg(z) = – \frac{\pi }{2}$.
Standard 11
Mathematics