1/2×4+1/3×5+1/4×6+1/5×7+……+1/8×10+1/9×11
问题描述：
1/2×4+1/3×5+1/4×6+1/5×7+……+1/8×10+1/9×11
答
以上数为列求和,每个数的分母都能写成n(n+2)即算式中每个数都可写作1/n(n+2) 其中n=2,3,4,5,6,7,8,9因2/n(n+2)=（n+2-n)/（n(n+2)）=(1/n)-(1/（n+2 ）)所以原式=（1/2-1/4+1/3-1/5+1/4-1/6+...+1/9-1/11)/2 =(1/2+1...