In Problems 1-2, find the maximum and minimum of the friction f over the closed and bounded set S. Use the methods of Section 12.8 to find the maximum and minimum on the interior of S; then use Lagrange multipliers to find the maximum and minimum over the boundary of S.
1. ((x, y) = 10 + x + y; S = {(x, y): x2 + y2 ( 1}
2. ((x, y) = x + y - xy; S = {(x, y): x2 + y2 ( 9}