Answer
$|3-6i|=3\sqrt{5}$
Work Step by Step
The plot of the given complex number, $ 3-6i ,$ is shown below.
The absolute value of the complex number $a+bi,$ written as $|a+bi|,$ is given by $\sqrt{a^2+b^2}.$ Therefore, the absolute value of the given complex number is \begin{align*} & \sqrt{(3)^2+(-6)^2} \\&= \sqrt{9+36} \\&= \sqrt{45} \\&= \sqrt{9}\cdot\sqrt{5} \\&= 3\sqrt{5} .\end{align*} Hence, $
|3-6i|=3\sqrt{5}
.$