The hypotenuse of a right-angled triangle is 12cm in length. Find the measure of the angles in the triangle that maximize its perimeter.

This is my function for perimeter that I came up with

12 + 12sin(theta)+12cos(theta)

Derivative

12cos(theta)-12sin(theta)

Are you just supposed to know when cos(theta) = sin(theta) or is there a way of figuring it out in different situations?