## Algebra: A Combined Approach (4th Edition)

The length of the unknown side is $3\sqrt{5}$.
In the formula $a^2 + b^2 = c^2$, $c$ is the hypotenuse. Here, $a = 6$ and $b = 3$. We solve for c, the hypotenuse. Then $a^2 + b^2 = c^2$ becomes $6^2 +3^2 =c^2$ $36+9 =45$ $c^2 = 45$ $c = \sqrt{45} =\sqrt{9*5} = 3\sqrt5$