4x+y-9>=0 ,x-y-1

4x+y-9>=0 ,x-y-1
4x+y-9>=0 ,x-y-1

4x+y-9>=0 ,x-y-1
设t=x-3y,则x=t+3y
x代入得
4t+13y-9≥0即8t+26y-18≥0
t+2y-1≤0即-13t-26y+13≥0
两式相加得-5t-5≥0即t≤-1
所以最大值为-1