`b)a^6-a^4+2a^3+2a^2`
`=a^4(a^2-1)+2a^2(a+1)`
`=a^4(a-1)(a+1)+2a^2(a+1)`
`=(a+1)(a^5-a^4+2a^2)`
`=a^2(a+1)(a^3-a^2+2)`
`d)x^4+2x^3+2x^2+2x+1`
`=x^4+2x^3+x^2+x^2+2x+1`
`=x^2(x^2+2x+1)+(x^2+2x+1)`
`=(x^2+2x+1)(x^2+1)`
`=(x+1)^2(x^2+1)`
`f)x^5+x^4+x^3+x^2+x+1`
`=x^3(x^2+x+1)+(x^2+x+1)`
`=(x^2+x+1)(x^3+1)`
`=(x+1)(x^2+x+1)(x^2-x+1)`