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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
(b)Let $z = 0 + ib$, where $b > 0$. Then $z$lies on +ve $y$-axis and so $arg(z) = \frac{\pi }{2}$.
Standard 11
Mathematics