`a) x-1+x^(n+3)-x^n`
`=x-1+x^n. x^3-x^n`
`=x-1+x^n(x^3-1)`
`=x-1+x^n(x-1)(x^2+x+1)`
`=x-1+(x-1)(x^(n+2)+x^(n+1)+x^n)`
`=(x-1)(x^(n+2)+x^(n+1)+x^n+1)`
`b) x^64+x^32+1`
`=(x^32)^2+2.x^32+1-x^32`
`=(x^32+1)^2-(x^16)^2`
`=(x^32-x^16+1)(x^32+x^16+1)`
`=(x^32-x^16+1)(x^32+2.x^16+1-x^16)`
`=(x^32-x^16+1)[(x^16+1)^2-(x^8)^2]`
`=(x^32-x^16+1)(x^16-x^8+1)(x^16+x^8+1)`
`=...`
`=(x^32-x^16+1)(x^16-x^8+1)(x^8-x^4+1)(x^4-x^2+1)(x^2-x+1)(x^2+x+1)`