Question

It says to find the unknown side length. If necessary, write the answer in simplest radical form.

Answer 1

You'd use the Pythagorean theorem for this since it's a right triangle.
$a^2+b^2=c^2$
So plug in your given numbers to get: $9^2+40^2=x^2$
Then solve:
$81+1600=x^2$
$1681=x^2$
$\sqrt{1681}= \sqrt{x^2}$
$41=x$