1*2,2*3,3*4,4*5,5*6,…… 99 * 100, the reciprocal sum of the first 99 items

1*2,2*3,3*4,4*5,5*6,…… 99 * 100, the reciprocal sum of the first 99 items

Each item can be split into a part minus B part, and then offset each other, leaving only 1 minus 100 part