Use Lagrange multipliers to maximize f(x, y) = 5xy subject to x + y = 6- max f(x, y) = f(3, -3) = -45 max f(x, y) = f(-3, -3) = 45 max f(x, y) = f(-3, 3) = -45 max f(x, y) = f(3, 3) = 45