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已知x-y<=2，
13<=2x-1/2<=2x<=20，
求z<=3x-1/2y的值域
已知1<=x-y<=2，
13<=2x-1/2<=2x<=20，
求z=3x-1/2y的值域
13<=2x-1/2<=2x<=20，
求z<=3x-1/2y的值域
已知1<=x-y<=2，
13<=2x-1/2<=2x<=20，
求z=3x-1/2y的值域
题目出错了，看不清你的条件，与所求的。一般做这种题目用待定系数法。
a(x-y)+b(2x)=3x-1/2y得a=1/2,b=5/4;带原题,得
1/2(1<=x-y<=2)+5/4(13<=2x<=20)=> 67/4<=Z<=26
1/2(1<=x-y<=2)+5/4(27/2<=2x<=41/2)=> 139/8<=Z<=213/8
67/4<=Z<=26;且139/8<=Z<=213/8得139/8<=Z<=26