You can use trigonometry in two steps. First find an angle using those 2 lengths. Ten use that angle with one of the lengths to find the longest side.
I was trying to figure out the length of the hypotenuse of a right triangle with the other sides measuring 30 and 40. The problem wanted two ways to find the length of the hypotenuse, but the only way I could think of was the Pythagorean theorem. What is a second way? Thanks!