1/(1*3)+1/(3*5)+1/(5*7)+1/（7*9）...1/(199*201)=1/2(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9...+1/199-1/201)＝100/201怎么做的，说的明白就给你分我不需要分，谢谢1/(n×(n+2))＝1/2(1/n－1/(n+2))