1 /6×11+1/11×16+1/16×21+1/21×26+1/26×31+1/31×36 =

问题描述:

1 /6×11+1/11×16+1/16×21+1/21×26+1/26×31+1/31×36 =

1/n(n+5)=(1/5)[1/n-1/(n+5)]于是1/6x11=(1/5)x(1/6-1/11)……1/31x36=(1/5)x(1/31-1/36)于是1 /6×11+1/11×16+1/16×21+1/21×26+1/26×31+1/31×36 =(1/5)(1/6-1/11+1/11-1/16+1/16-1/21+1/21-1...