`(x^2 - x+2)(x-1) - x^2(1-x)^2 - (2x+1)(1-x)^3`
`= (x^2 - x + 2)(x-1) - x^2 (x-1)^2 + (2x+1)(x-1)^3`
`= (x-1) . [ (x^2- x+2) - x^2(x-1) + (2x+1)(x-1)^2]`
` = (x-1) . [x^2 - x + 2 - x^3 + x^2 + (2x+1)(x^2 - 2x+1)]`
` = (x-1) . (- x^3 + 2x^2 - x + 2 + 2x^3 - 4x^2 + 2x + x^2 - 2x + 1)`
` = (x-1). (x^3 -x^2 -x+3)`