I'm in a bit of a hurry, so this isn't going to be very pretty. 1. The problem statement, all variables and given/known data Maximize: V(l,d) = pi * (0.5*d)^2 * l Subject to: l + 3.5d = 84 -> C(l, d) = l + 3.5d - 84 2. Relevant equations ∇V(l,d) = λ ∇C(l,d) 3. The attempt at a solution ∇V(l,d) = 0.5*pi*d ∇C(l,d) = 0 How do I find the Lagrange multiplier if the gradient of the condition-function is 0? I have to find the optimal conditions using Lagrange's method. I have already found the optimal conditions using the method involving elimination of variables, which gave me l = 28 and d = 26. Now I have to get the same results using this method. EDIT: Nevermind. I figured out my stupid mistake.