`text{Đáp án:}`
`a) (6x + 30)/7`
`b) (12x^2 + 7x - 10)/12`
`text{Giải thích các bước giải:}`
`a) 6/7 (5 + x)`
`= 6/7 (x + 5)`
`= (6(x + 5))/7`
`= (6x + 30)/7`
`b) (x - 2/3)(x + 5/4)`
`x(x + 5/4) - 2/3 (x + 5/4)`
`x^2 + 5/4x - 2/3 (x + 5/4)`
`x^2 + (5x)/4 - 2/3 (x + 5/4)`
`(4x^2)/4 + (5x)/4 - 2/3(x + 5/4)`
`(4x^2 + 5x)/4 - 2/3(x + 5/4)`
`(4x^2 + 5x)/4 - (-2(x + 5/4))/3`
`(4x^2 + 5x)/12 - (-2x - 5/4)/12`
`(4x^2 + 5x + -2x - 5/4)/12`
`(12x^2 + 15x - 8x - 10)/12`
`(12x^2 + 7x - 10)/12`
