`a, (x + y)(x + y) = (x + y)^2 = x^2 + 2xy + y^2`
`b, (x - y)(x - y) = (x - y)^2 = x^2 - 2xy + y^2`
`c, (x - y)(x + y) = x^2 - y^2`
`d, (x + y)(x + y)(x + y) = (x + y)^3 = x^3 + 3x^2y + 3xy^2 + y^3`
`e, (x - y)(x - y)(x - y) = (x - y)^3 = x^3 - 3x^2y + 3xy^2 - y^3`
`f, (x + y)(x^2 - xy + y^2) = x^3 + y^3`
`g, (x - y)(x^2 + xy + y^2) = x^3 - y^3`