need a formula for triangle

hi i need to find the angle theta that maximizes the area of the isosceles triangle with legs length L. Once I can get a formula, I am fine to calculate the derivatives and determine the maximum, but my trig is a little rusty, especially with angles.

I need to know how to find the formula to express the area in terms of the angle, theta (theta is between the two identical sides of the isosceles).

thanks

alright, so next question

if i use the formula above to express area and take the derivative of said formula, will the derivative be cos(theta)? do I treat L as a constant?