-1/2 ×1/(1+x/2)=-1/2 ×∑(n=0从∞)(-x/2)^n=-∑(n=0从∞)(-1)^n/(2^(n+1)) x^n原式=【-∑(n=0从∞)(-1)^n/(2^(n+1)) x^n】'=-∑(n=1从∞)(-1)^n· n/(2^(n+1)) x^(n-1)
