已知x:y:z=3:4:7,且2x—y+z=-18,求式子x+2y-z的值.
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已知x:y:z=3:4:7,且2x—y+z=-18,求式子x+2y-z的值.
![已知x:y:z=3:4:7,且2x—y+z=-18,求式子x+2y-z的值.](/uploads/image/z/15434940-12-0.jpg?t=%E5%B7%B2%E7%9F%A5x%3Ay%3Az%3D3%3A4%3A7%2C%E4%B8%942x%E2%80%94y%2Bz%3D-18%2C%E6%B1%82%E5%BC%8F%E5%AD%90x%2B2y-z%E7%9A%84%E5%80%BC.)
设x=3a,y=4a,z=7a
带入2x—y+z=-18
求得a=2
所以x+2y-z=4a=8
带入2x—y+z=-18
求得a=2
所以x+2y-z=4a=8
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