若x+y+z=30,3x+y-z=50.x,y,z均为非负数,则M=5x+4y+2z的取值范围是xiexie
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若x+y+z=30,3x+y-z=50.x,y,z均为非负数,则M=5x+4y+2z的取值范围是xiexie若x+y+z=30,3x+y-z=50.x,y,z均为非负数,则M=5x+4y+2z的取值范
若x+y+z=30,3x+y-z=50.x,y,z均为非负数,则M=5x+4y+2z的取值范围是xiexie
若x+y+z=30,3x+y-z=50.x,y,z均为非负数,则M=5x+4y+2z的取值范围是
xiexie
若x+y+z=30,3x+y-z=50.x,y,z均为非负数,则M=5x+4y+2z的取值范围是xiexie
(110,140)用扩大缩小方法
由前两个式子,把y,z用x表示得
y=40-2x
z=x-10
所以 10 <= x <= 20
M=3( X+Y+Z)+(3X+Y-Z)-X
=90+50-X
=140-x
所以 120 <= M <= 130
M=5X+4Y+2Z=8X+4Y+2Z-3X=2(4X+2Y)+2Z-3X,因为
x+y+z=30
3x+y-z=50
所以4X+2Y=80,所以M=160-(3X-Z)+Z=160-(50-Y)+Z=110+Y+Z=140-X
因为X为非负数,且3x+y-z=50,所以X的取值范围是(0,50/3),所以
M的取值范围是(370/3,140)
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