Which of the following is correct for any two complex numbers

Question:

Which of the following is correct for any two complex numbers z1 and z2?

(a) $\left|z_{1} z_{2}\right|=\left|z_{1}\right|\left|z_{2}\right|$

(b) $\arg \left(z_{1} z_{2}\right)=\arg \left(z_{1}\right) \arg \left(z_{2}\right)$

(c) $\left|z_{1}+z_{2}\right|=\left|z_{1}\right|+\left|z_{2}\right|$

(d) $\left|z_{1}+z_{2}\right| \geq\left|z_{1}\right|+\left|z_{2}\right|$

Solution:

Since, it is known that

$\left|z_{1} z_{2}\right|=\left|z_{1}\right|\left|z_{2}\right|$

$\arg \left(z_{1} z_{2}\right)=\arg \left(z_{1}\right)+\arg \left(z_{2}\right)$ and

$\left|z_{1}+z_{2}\right| \leq\left|z_{1}\right|+\left|z_{2}\right|$

Hence, the correct option is (a) .

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