`x^3 - 2x^2y + xy^2 - 9x`
` = x (x^2 - 2xy + y^2 - 9)`
` = x [ (x^2 - 2xy + y^2) - 9]`
` = x [ (x-y)^2 - 3^2]`
` = x (x-y-3)(x-y+3)`
``
`x^7 + x^2 + 1`
` = (x^7 - x^6 + x^4 - x^3 + x^2) + (x^6 - x^5 + x^3 - x^2 + x) + (x^5 -x^4 + x^2 - x +1)`
`= x^2 (x^5 -x^4 + x^2 - x +1) + x(x^5 -x^4 + x^2 - x +1) + (x^5 -x^4 + x^2 - x +1)`
` = (x^2 + x +1)(x^5 -x^4 + x^2 - x +1)`