Find the length of the third side. If necessary, round to the nearest tenth.

18.3
Step-by-step explanation:
a^2 = b^2 + c^2
a is always the hypotenuse so a^2 - b^2 = c^2
If you plug that into your calculator as 25^2 - 17^2 you'll get 336 so now we know that c^2 = 336 so to get c we plug √336 into the calculator and get 18.33030278 which to the nierest 10th which is 18.3

^2 means squared
√ means squared root