f（x）的n阶导数是n!/(1-x)^(n+1),代入x=-1得n!/2^(n+1),所以泰勒系数是n!/[n!·2^(n+1)]=
1/2^(n+1),所以展式为：Σ[1/2^(n+1)](x+1)^n,求和从0到+∞