`a)`
`x/(x - 1) + (x + 3)/(x^2 - 1) + 1/(x + 1) (đk x \ne ± 1)`
`= (x(x + 1))/((x + 1)(x - 1)) + (x + 3)/((x + 1)(x - 1)) + (x - 1)/((x + 1)(x - 1))`
`= (x^2 + x + x + 3 + x - 1)/((x + 1)(x - 1))`
`= (x^2 + 3x + 2)/((x + 1)(x - 1))`
`= (x^2 + x + 2x + 2)/((x + 1)(x - 1))`
`= ((x + 1)(x + 2))/((x + 1)(x - 1))`
`= (x + 2)/(x - 1)`
`b)`
`(x + 10)/(x - 2) + (x - 18)/(x - 2) + (x + 2)/(x^2 - 4) (đk x \ne ± 2)`
`= (x + 10 + x - 18)/(x - 2) + (x + 2)/((x + 2)(x - 2))`
`= (2x - 8)/(x - 2) + (x + 2)/((x + 2)(x - 2))`
`= ((2x - 8)(x + 2))/((x + 2)(x - 2)) + (x + 2)/((x + 2)(x - 2))`
`= (2x^2 - 4x - 16 + x + 2)/((x + 2)(x - 2))`
`= (2x^2 - 3x - 14)/((x + 2)(x - 2))`
`= (2x^2 + 4x - 7x - 14)/((x + 2)(x - 2))`
`= ((2x - 7)(x + 2))/((x + 2)(x - 2))`
`= (2x - 7)/(x - 2)`
