1=xy/x+y,2=yz/y+z,3=zx/z+x,则x+y+z的值为( ).A.276/35 B.-276/35 C.11/12 D.-11/12
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![1=xy/x+y,2=yz/y+z,3=zx/z+x,则x+y+z的值为( ).A.276/35 B.-276/35 C.11/12 D.-11/12](/uploads/image/z/6956748-36-8.jpg?t=1%3Dxy%2Fx%2By%2C2%3Dyz%2Fy%2Bz%2C3%3Dzx%2Fz%2Bx%2C%E5%88%99x%2By%2Bz%E7%9A%84%E5%80%BC%E4%B8%BA%EF%BC%88+%EF%BC%89.A.276%2F35+B.-276%2F35+C.11%2F12+D.-11%2F12)
1=xy/x+y,2=yz/y+z,3=zx/z+x,则x+y+z的值为( ).A.276/35 B.-276/35 C.11/12 D.-11/12
1=xy/x+y,2=yz/y+z,3=zx/z+x,则x+y+z的值为( ).A.276/35 B.-276/35 C.11/12 D.-11/12
1=xy/x+y,2=yz/y+z,3=zx/z+x,则x+y+z的值为( ).A.276/35 B.-276/35 C.11/12 D.-11/12
(x+y)/xy=1
(y+z)/yz=1/2
(z+x)/zx=1/3
就是说
1/x+1/y=1
1/y+1/z=1/2
1/z+1/x=1/3
上面分别代入下面
1/x+1/y+1/z=11/12
得出1/x=5/12,1/y=7/12,1/z=-1/12
得出
z=-12 y=12/7 x=12/5
x+y+z=-276/35
选B
根据题目可以知道
(x+y)/xy=1
(y+z)/yz=1/2
(z+x)/zx=1/3
就是说
1/x+1/y=1
1/y+1/z=1/2
1/z+1/x=1/3
可以分别计算出1/x,1/y,1/z
选b
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