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