Find the square root of a term with a variable

Question

I'm reviewing a PSAT score report with my son and trying to account for the College Board's answer.

Below are the question and answer. I follow them as far as: $$ \sqrt{8r^2} $$

From that point, I would simplify something like this: $$ \sqrt{2(2^2)(r^2)} $$ $$ 2r\sqrt{2} $$

But the answer is:

$$ 2\sqrt{2r} $$

I don't understand how the square root of $r^2$ becomes the square root of r.

Please explain or point me to an explanation online. I'm clearly no mathematician.

Answer 1

There is a printing error;

usually one write $\sqrt{8} = 2\sqrt{2}$, so $\sqrt{8r^2} = 2\sqrt 2 r $ may easily have become $2\sqrt{2r}$