Question

Which of the following is an example of a complex number that is not in the set of real numbers?

Answer 1

A complex number has a real and an imaginary part

$4 + 9i$ is a complex number

A complex number is represented as:

$a + bi$

Where:

$a \to$ real

$bi \to$ imaginary

By comparing the options to $a + bi$;

$-7$ and $2 + \sqrt 5$ are not complex numbers

This is so because they do not have imaginary parts

However,

$4 + 9i$ is a complex number

Because; 9i is imaginary

Read more about complex numbers at:

brainly.com/question/19007885