# Thread: need a formula for triangle

1. ## 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

2. If length of two identical sides is L and the angle between them is θ, the area is $\displaystyle A = \frac {1}{2} L^2 sin(\theta)$

3. ## 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?

4. Originally Posted by lostderiv
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?
Originally Posted by lostderiv
hi i need to find the angle theta that maximizes the area of the isosceles triangle with legs length L.
That seems to be the problem you posted, so I would say yes.

-Dan