题目有问题,yx/(y+x)=4/3应该是yz/(y+z)=4/3xy/(x+y)=-2(x+y)/(xy)=-1/21/x +1/y=- 1/2 (1)yz/(y+z)=4/3(y+z)/(yz)=3/41/y +1/z=3/4 (2)zx/(z+x)=-4/3(z+x)/(zx)=-3/41/x +1/z=-3/4 (3)(1)+(2)+(3)2(1/x+ 1/y+ 1/z)=...不明白(x+y)/(xy)=-1/2 1/x +1/y=- 1/2 为什么两条算式的答案是一样的呢？这不是两条算式，而是等式的变形。(x+y)/(xy)=x/(xy) +y/(xy)=1/y +1/x1/x +1/y=-1/2