`3a^2 - 3ab + b - a`
`= 3a(a - b) - (a - b)`
`= (3a - 1)(a - b)`
`x^2 + x - (x + 1)y`
`= x(x + 1) - (x + 1)y`
`= (x + 1)(x - y)`
`2x^2 + 4ax + x + 2a`
`= 2x(x + 2a) + (x + 2a)`
`= (2x + 1)(x + 2a)`
`x^2y^2 + y^3 + zx^2 + yz`
`= y^2(x^2 + y) + z(x^2 + y)`
`= (y^2 + z)(x^2 + y)`