Find the coefficient of 1 / x ^ 6 in (1 + 2 / x ^ 2) ^ 5 expansion

Find the coefficient of 1 / x ^ 6 in (1 + 2 / x ^ 2) ^ 5 expansion

eighty

What is the coefficient of x ^ 3 in {(1 + x) ^ 6} (1-x) ^ 5 expansion?

C(3,6)*C(0,5)+C(2,6)*C(1,5)*(-1)+C(1,6)*C(2,5)*(-1)^2+C(0,6)*C(3,5)*(-1)^3
=20-15*5+6*10-10=-5

The first n terms of sequence {an} and an = - 12n2 + kn (where k ∈ n +) are known, and the maximum value of an is 8; the first n terms of sequence {BN} and BN = n + 23bn, and B1 = 1. (1) determine the constant K and find an; (2) find the first n terms and Sn of sequence {BN (9-2an) 4N}

(1) The first n terms of ∵ sequence {an} and an = - 12n2 + kn (where k ∈ n +), and the maximum value of an is 8, then K ∈ n *, so when n = k, the maximum value of an is 12k2 = 8, the solution is k = 4, when n ≥ 2, an = an-an-1 = (- 12n2 + 4N) - [- 12 (n-1) 2 + 4 (n-1)] = - N + 92, when n = 1, A1 = 72, suitable for