... 1 .2. 2 n 2 C2 + 2. 3 .2 n −3 C3 + + (n − 1)nCn = n(n − 1)3n 2 n n n ⇔ n −1 C2 + 3 .2 n 2 C3 + 3.4 .2 n − C + + (n − 1)nCn = n(n − 1)3n 2 n n n n d) Với a = 2, x = –1, ta : 1 .2. 2 n 2 C2 − 2. 3 .2 ... = n(n − 1 )2 n 2 n n n n b) 1.2C2 − 2. 3C3 + + (−1)n 2 (n − 1)nC n = n n c) n −1 C2 + 3 .2 n 2 C3 + 3.4 .2 n − C n + + (n − 1)nCn = n(n − 1)3n 2 n n n d) n −1 C2 − 3 .2 n 2 C3 + 3.4 .2 n − Cn ... 2 n n a) Với a = 1, x = 1, ta : 1.2C2 + 2. 3C3 + + (n − 1)nCn = n(n − 1 )2 n 2 n n n b) Với a = 1, x = – 1, ta : n 1.2C2 − 2. 3C3 + + (−1)n 2 (n − 1)nC n = n n c) Với a = 2, x = 1, ta : 1 .2. 2...