Start by letting L = 4r. You then have a function in two unknowns. The maximum will be at points where the partial derivatives are 0 and the Hessian is negative definite, or if you can show the function is concave at that point.
Start by letting L = 4r. You then have a function in two unknowns. The maximum will be at points where the partial derivatives are 0 and the Hessian is negative definite, or if you can show the function is concave at that point.