Đáp án+Giải thích các bước giải:
`A=(x^3-x)/((1+xy)^2-(x+y)^2)`
`a)ĐK:(xy+1)^2-(x+y)^2\ne0`
`<=>(xy+1-x-y)(xy+1+x+y)\ne0`
`<=>[x(y-1)-(y-1)][x(y+1)+y+1]\ne0`
`<=>(x-1)(y-1)(x+1)(y+1)\ne0`
`<=>{(x-1\ne0),(y-1\ne0),(x+1\ne0),(y+1\ne0):}`
`<=>x,y ne +-1`
`b)A=(x^3-x)/((1+xy)^2-(x+y)^2)`
`A=(x(x^2-1))/((xy+1-x-y)(xy+1+x+y))`
`A=(x(x-1)(x+1))/[[x(y-1)-(y-1)][(x(x+1)+y+1]]`
`A=(x(x-1)(x+1))/((x-1)(y-1)(x+1)(y+1))`
`A=x/((y-1)(y+1))`
`c)x=-60,y=99`
`=>A=(-60)/((99-1)(99+1))`
`=>A=(-60)/(98.100)`
`=>A=(-3.10.2)/(49.2.10.10)`
`=>A=-3/(490)`
