x^3+y^3+z^3=(x+y)^3+z^3-3xy(x+y)=(x+y+z)^3-3z(x+y)(x+y+z)-3xy(x+y)=(x+y+z)^3-3(x+y)(xz+yz+z^2+xy)=(x+y+z)^3-3(x+y)(z+x)(z+y)
(X+Y+Z)(X^2+Y^2+Z^2-XZ-XY-YZ)+3XYZ