`i)=x^5+x^4+x^3-x^3-x^2-x+x^2+x+1`
`=x^3(x^2+x+1)-x(x^2+x+1)+(x^2+x+1)`
`=(x^3-x+1)(x^2+x+1)`
`k) =x^4+4x^2 . y^2 +4y^4-4x^2y^2`
`=(x^2+2y^2)^2-(2xy)^2`
=(x^2+2y^2-2xy)(x^2+2y^2+2xy)`
`l) =x^4+2x^y^2+y^3-x^2y^2`
`=(x+y^2)^2-(xy)^2`
`=(x^2+y^2-xy)(x^2+y^2+xy)`