∑【un+un+1】收敛于2s-u1怎么做的呢？解释下理由好吗？谢谢∑【un+un+1】 =∑(n从1到∞)un+∑(n从1到∞)un+1 =s+∑(n从1到∞)un+1 (后面相当于从u2开始相加，所以可化为∑(n从1到∞)un-u1) =s+∑(n从1到∞)un-u1 =s+s-u1 =2s-u1