calculus
posted by soffy .
to find the possible relative extrema of the function f(x,y) subject to the constraint g(x,y)=8, the lagrangian function based on the lagrange multiplier λ is given by....

solve the equations
∇f(x,y) = λ∇g(x,y)
g(x,y) = 8
plug in the solutions and pick the extrema.