Answer
$$b=15$$
Work Step by Step
Use the Pythagorean Theorem:
$$c^{2}=a^{2}+b^{2}.$$
Rearrange terms:
$$b^{2}=c^{2}-a^{2}.$$
Substitute in $a=8$ and $c=17:$
$$b^{2}=17^{2}-8^{2}=289-64=225.$$
Take the square root of both sides:
$$\sqrt {b^{2}}=\sqrt {225}$$
$$b=15.$$
