MCQ - 474-9206

Correct Answer: D

Explanation:

We are looking for a number that is not real.

${\displaystyle 4\mathrm{\pi <!--\; \pi \; -->}}$, ${\displaystyle 6e}$, and ${\displaystyle \sqrt{84}}$ are irrational numbers, but they are still real.

Then, ${\displaystyle 4i^2}$ is equivalent to −4 by the rules of complex numbers. Thus, it is also real.

That leaves us with: ${\displaystyle \sqrt{-<!--\; -\; -->9}}$ which in fact is imaginary (since no real number multiplied by itself yields a negative number) and simplifies to ${\displaystyle 3i}$.