120到130 .
由x+y+z=30①,3x+y-z=50 ② ②-①得x-z=10 .因为x,y,z都是大于等于0所以z>=0
①+②=4x+2y=80 推出x
已知x+y+z=30,3x+y-z+50,x.y.z皆为非负数,求m=5x+4y+2z的取值范围.
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