已知x+y+z=30,3x+y-z=50,xyz皆为非负数,求m=5x+4y+2z的取值范围
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已知x+y+z=30,3x+y-z=50,xyz皆为非负数,求m=5x+4y+2z的取值范围
已知x+y+z=30,3x+y-z=50,xyz皆为非负数,求m=5x+4y+2z的取值范围
已知x+y+z=30,3x+y-z=50,xyz皆为非负数,求m=5x+4y+2z的取值范围
x+y+z=30
3x+y-z=50
5x+4y+2z=m
把m当作常数,解此方程组
x=140-m
y=-240+2m
z=130-m
因为x,y,z,均为非负数
140-m>=0
-240+2m>=0
130-m>=0
所以m=120,m
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