Rút gọn

)C = 6(c – d)(c + d)2 + 12(c – d)2(c + d) + (c + d)3 + 8(c – d)3;
b) D = (m – n)3 – (n + p)3 -3(n + p)2(n – m) – 3(n + p)(n – m)2.