Đáp án+Giải thích các bước giải:
`1/(x(x+y)) + 1/(y(x+y)) + 1/(x(x-y)) + 1/(y(y-x))`
`=y/(xy(x + y)) + x/(xy(x + y)) + 1/(x(x-y)) + 1/(y(y-x))`
`=y/(xy(x + y)) + x/(xy(x + y)) + 1/(x(x-y)) - 1/(y(x-y))`
`= (y+x)/(xy(x + y))+ y/(yx(x - y)) - x/(xy(x - y))`
`= 1/(xy)+ (y-x)/(xy(x - y))`
`= 1/(xy)- ( x- y)/(xy(x - y))`
`= 1/(xy) - 1/(xy)`
`= 0`
Xin hay nhất