Question

问一道数学计算题啊.话说这题算出来不应该是1+1/2-1/10-1/11 不对么TAT,.为什么我就算不出来正确答案呢、

Answer 1

1/1*3+1/2*4+1/3*5+1/4*6+……+1/9*11

=(1/1*3+1/3*5+...+1/9*11)+(1/2*4+1/4*6+...+1/8*10)

=(1/1-1/3+1/3-1/5+...+1/9-1/11)/2+(1/2-1/4+1/4-1/6+...+1/8-1/10)/2

=(1-1/11)/2+(1/2-1/10)/2

=10/11*1/2+4/10*1/2

=5/11+1/5

=36/55