Question

Two complex numbers are represented by ordered pairs $z_1:(2,4)\&z_2:(-4,5)$, which of the following is imaginary part of $z_1\times z_2=$?

• A. $-28$
• B. $6$
• C. $-6$
• D. None of these

Answer 1

The correct option is C $-6$

$z_1$ is $2+4i$ and $z_2$ is $-4+5i$, where $i=\sqrt{-1}$

$z_1\times z_2=(2+4i)(-4+5i)$

$=-8+10i-16i+20i^2$

$=-28-6i$ ........(Since $i^2=-1$)

Thus the imaginary part is $-6$.