`a)`
`A=1/(x-1)-1/(x+1)+(4x+2)/(x²-1)` `ĐK:x\ne±1`
`=(x+1)/((x-1)(x+1))-(x-1)/((x-1)(x+1))+(4x+2)/((x-1)(x+1))`
`= ((x+1)-(x-1)+(4x+2))/((x-1)(x+1))`
`=(x+1-x+1+4x+2)/((x-1)(x+1))`
`=(4x+4)/((x-1)(x+1))`
`=(4(x+1))/((x-1)(x+1))`
`=4/(x-1)`
`b)`
`Để` `A=4/(2015)`
`⇔4/(x-1)=4/2015`
`⇔4(x-1)=4×2015`
`⇔x-1=2015`
`⇔x=2016` `(tm)`
`Vậy....`
