若x+y+z=30,3x+y-z=50,x,y,z都为非负实数,则M=5x+4y+2z的取值范围是______.
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若x+y+z=30,3x+y-z=50,x,y,z都为非负实数,则M=5x+4y+2z的取值范围是______.
由题意得
x+y+z=30 ①
3x+y−z=50 ②,且x≥0,y≥0,z≥0
由②-①得 x-z=10,
即x=10+z
由①×3-②得 2y+4z=40,
即y=20-2z,
又∵x≥0,y≥0,z≥0,
∴0≤z≤10,
∵M=5x+4y+2z=(2x+2y+2z)+(3x+y-z)+(y+z)=130-z,
∴120≤M≤130.
故答案为:120≤M≤130.
x+y+z=30 ①
3x+y−z=50 ②,且x≥0,y≥0,z≥0
由②-①得 x-z=10,
即x=10+z
由①×3-②得 2y+4z=40,
即y=20-2z,
又∵x≥0,y≥0,z≥0,
∴0≤z≤10,
∵M=5x+4y+2z=(2x+2y+2z)+(3x+y-z)+(y+z)=130-z,
∴120≤M≤130.
故答案为:120≤M≤130.
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