L=100x十80y-C∂L/∂x=100-∂C/∂x=0,∂C/∂x=100∂L/∂y=80-∂C/∂y=0∂C/∂y=80边际收入=边际成本时，总利润最大。∂C/∂x=40十0.2x=100,x=60/0.2=300∂C/∂y=30十0.2y=80y=50/0.2=250
