xy(x + y) + yz(y + z) + xz(x + z) + 2xyz
= x 2 y + x y 2 + yz(y + z) + x 2 z + x z 2 + xyz + xyz
= ( x 2 y + x 2 z) + yz(y + z) + (x y 2 + xyz) + (x z 2 + xyz)
= x 2 (y + z) + yz(y + z) + xy(y+ z) + xz(y + z)
= (y + z)( x 2 + yz + xy + xz) = (y + z)[( x 2 + xy) + (xz + yz)]
= (y + z)[x(x + y) + z(x + y)] = (y + z)(x+ y)(x + z)