Sometimes you may wish to find the relative maxima or minima of f(x, y) = 0 subject to some constraint condition φ(x, y) = 0. To do this, form the function h(x, y) = f(x, y) + λφ(x, y) and set
The constant λ is called a Lagrange multiplier and the method is called the method of Lagrange multipliers.
