(x+y)³ = (x+y) (x+y) (x+y)
it really is just whatever is within the parenthesis times itself 3 times
(x+y)³ =(x^2+2xy+y^2)(x+y)
foil the first 2
(x+y)³ =x^3+2x^2y+xy^2+x^2y+2xy^2+y^3
then foil 3rd one
(x+y)³ = x^3+3x^2y+3xy^2+y^3
then you put like terms together