# Thread: Max/Min using Lagrange Multiplier Method

1. ## Max/Min using Lagrange Multiplier Method

Problem: Find the absolute maximum and minimum values for f(x,y) = sin x + cos y on the rectangle R defined by 0<=x<=2pi and 0<=y<=2pi using the method of Lagrange Multipliers.

I'm having trouble putting the constraints into something I can work with.
I know gradient[f(x,y)] = lambda1*gradient[g1] + lambda2*gradient[g2], but what are my g1 and g2 functions? Thanks

2. Originally Posted by andrewjohnsc
Problem: Find the absolute maximum and minimum values for f(x,y) = sin x + cos y on the rectangle R defined by 0<=x<=2pi and 0<=y<=2pi using the method of Lagrange Multipliers.

I'm having trouble putting the constraints into something I can work with.
I know gradient[f(x,y)] = lambda1*gradient[g1] + lambda2*gradient[g2], but what are my g1 and g2 functions? Thanks
It is absurd to try solving this using Lagrange Multiplers since the minimum is obviously -2 and the maximum is +2 and because of the periodic nature of f(x,y) these can be found by conventianal calculus techniques.

If you decide to go down the route of Lagrange Multipliers you first have to look for the calculus like extrema without constraints. In which case you will find the extrem values mentioned above, and as at least one point exists in the feasible region for each, and they are obviously global maximum and mininum you are done before introducing any multipliers.

CB