Hoặc
c) x3 + y3 + 4x + 4y;
c) x3 + y3 + 4x + 4y
= (x3 + y3) + (4x + 4y)
= (x + y)(x2 – xy + y2) + 4(x + y)
= (x + y)(x2 − xy + y2 + 4).