(1) (3a + 4b)3 = 3C0 (3a)3 + 3C1 (3a)2 (4b) + 3C2 (3a)1 (4b)2 + 3C3 (4b)3
= 1 × 27a3 + 3 × 9a2 × 4b + 3 × 3a × 16b2 + 1 × 64b3
= 27a3 + 108a2b + 144ab2 + 64b3
(2) (1 + x)7 = 7C0 (1)7 + 7C1 (1)6 (x) + 7C2 (1)5 (x2) + 7C3 (1)4 (x)3 + 7C4 (1)3 (X4) + 7C5 (1)2 (x5)
7C6 (1) (x6) + 7C7 (x7)
= 1 × 1 + 7 × 1 × x + 21 × 1 × x2 + 35 × 1 × x3 + 35 × 1 × x4 + 21 × 1 × x5 7 × 1 × x2 + 1 × x7
= 1 + 7x + 21x2 + 35x3 + 35x4 + 21x5 + 7x6 + x7