A+b)n power = c (n, 0) a (n power) +C(n, 1)a(n- 1 power) b( 1 power) +…+C(n, r)a(n-r).

C(n, 0) represents 0 in n,

This formula is called binomial theorem, and the polynomial on the right is called quadratic expansion of (a+b)n, where the coefficient CNR (r = 0, 1, ... n) is called quadratic coefficient, and Cnran-rbr in the formula is called the general term of binomial expansion, which is expressed by Tr+ 1, that is, the general term is expansion.

explain

(1) tr+ 1 = CNRAA-RBR is the r+ 1 term of (a+b+a)n n expansion, R = 0, 1, 2 ... n. It and (b+a+b) n n.

②Tr+ 1 only refers to the standard form of (a+b)n, and the binomial expansion formula of (a-b)n is tr+1= (-1) rcnran-rbr.

(3) The coefficient Cnr is called the r+ 1 binomial coefficient of the expansion, which should be distinguished from the r+ 1 binomial coefficient about a letter (or letters).

It's so complicated, in fact, the simplest thing is to calculate a-b honestly and then N-power.