a) `(x+1)(x+3) - x(x+2) =7`
`=>( x^2 + 3x + x + 3) -(x^2 + 2x) =7`
`=> x^2 + 4x + 3 - x^2 -2x =7`
`=> (x^2 - x^2) + (4x - 2x) + 3=7`
`=> 2x= 4`
`=> x= 4:2`
`=> x= 2`
Vậy `x= 2`
b) `2x(3x+5) - x(6x -1) =33`
`=> (6x^2 + 10x) - (6x^2 - x) =33`
`=> 6x^2 + 10x - 6x^2 + x =33`
`=> (6x^2 - 6x^2) + (10x + x) =33`
`=> 11x= 33`
`=> x= 33:11`
`=> x= 3`
Vậy `x=3`