IL} The trough in the gure is to be made to the dimensions shown. Only the angle 0 can be varied. What value of 0 will maximize the trough's volume?

Hi! I attached one of my homework questions on optimization. I'm having a hard time understand why my answers are incorrect. I got pi/6 the first time and pi/2 the second time; but both of them are wrong. Please help! thank you!