Đáp án:
`a, (x^2 + 7x + 12)/(4x^2 + 12x)`
`= ((x^2 + 6x + 9) + (x + 3))/(4x(x + 3))`
`= ((x + 3)^2 + (x + 3))/(4x(x + 3))`
`= ((x + 3)(x + 3 + 1))/(4x(x + 3))`
`= ((x + 3)(x + 4))/(4x(x + 3))`
`= (x + 4)/(4x)`
`b, (5x^3 - 20x)/(x^2 - x - 2)`
`= (5x(x^2 - 4))/(x^2 - 2x + x - 2)`
`= (5x(x - 2)(x + 2))/(x(x - 2) + (x - 2))`
`= (5x(x - 2)(x + 2))/((x - 2)(x + 1))`
`= (5x(x + 2))/(x + 1)`
`= (5x^2 + 10x)/(x + 1)`
`c, (x^2 - 8x + 12)/(x^2 - 2x - 24)`
`= (x^2 - 2x - 6x + 12)/(x^2 - 6x + 4x - 24)`
`= (x(x - 2) - 6(x - 2))/(x(x - 6) + 4(x - 6))`
`= ((x - 2)(x - 6))/((x - 6)(x + 4))`
`= (x - 2)/(x + 4)`
`d, (4x^2 - 12x + 9)/(2x^2 - 13x + 15)`
`= ((2x)^2 - 2.2x.3 + 3^2)/(2x^2 - 3x - 10x + 15)`
`= ((2x - 3)^2)/(x(2x - 3) - 5(2x - 3))`
`= ((2x - 3)^2)/((2x - 3)(x - 5))`
`= (2x - 3)/(x - 5)`
