The legs of a triangle measure 13 cm and 17 cm which of the following is the measure for the longest side of the triangle

You would use the Pythagorean Theorem to solve this which is (leg squared)x(leg squared)=(hypotenuse or the longest side)
Your answer would be 21.4
Hope This Helps.

C≈21.40093455,−21.40093455 that should be the right answer