(x + a)^n = x^n + nax^(n-1) + n(n-1)a^2x^(n-2)/2 + ...+ n!/[k!(n-k)!]a^kx^(n-k) + ...+ nxa^(n-1) + a^n 1,a^n = (0 + a)^n,令x = 0,带入即可.2,x的k次方的系数 = n!/[k!(n-k)!]a^(n-k) 3,(x + a)^n + (x + b)^...