Answer:
Pythagorean theorem: a^2 + b^2 = c^2
c is always the hypotenuse (longest side of the triangle)
Plug the numbers in:
17^2 + ?^2 = 19^2
?^2 = 19^2 - 17^2
?^2 = 361 - 289
?^2 = 72
? = 8.48528137424
