已知x分之1减y分之1等于7,求(x方+y方)除以xy
问题描述:
已知x分之1减y分之1等于7,求(x方+y方)除以xy
答
解
1/x-1/y=7
(y-x)/xy=7
y-x=7xy
∴(x²+y²)/xy
=[(x-y)²+2xy]/xy
=[(y-x)²+2xy]xy
=(49xy+2xy)/xy
=(51xy)/xy
=51(y-x)²怎么会是49xy。应该是49(xy)²嗯嗯,是我算错了
=(49x²y²+2xy)xy
=49xy+2我算出来也是这样的,可不可以再简便一点啊,算到最后直接是数字的?