Originally Posted by yellowjellybean
Oh I see, if we assume it's a right triangle, the 100 would be the hypotenuse. But I don't understand from where in the question, we can just assume that.
We know the angle for the unknown is 30 so that can't be the hypotenuse. That leaves 87 and 100 and the longest side is always the hypotenuse in a right triangle because it is produced by the largest possible angle, 90.