x－y分之1减x+y分之1等于多少?

题目

x－y分之1减x+y分之1等于多少?

答案

1/(x-y)- 1/(x+y)原式=(x+y)/(x-y)(x+y)- (x-y)/(x-y)(x+y) =(x+y)-(x-y)/(x-y)(x+y) =x+y-x+y/(x-y)(x+y) =2y/(x-y)(x+y)【也可写成2y/x^2-y^2,这是平方差公式,楼下的是...