a) \(=(x^2y+xy^2+xyz)+(x^2z+xz^2+xyz)+(yz^2+y^2z+xyz)\)
\(=xy(x+y+z)+xz(x+z+y)+yz(z+y+x)\)
\(=(xy+xz+yz)(x+y+z)\)
Câu b xem lại coi!! Cảm giác sai sai :)))
c) \(=(x+y)^3-3xy(x+y)+3xy-1\)
\(=(x+y-1)(x^2+2xy+y^2-x-y+1)-3xy(x+y-1)\)
\(=(x+y-1)(x^2-xy+y^2-x-y-1)\)