分母分别是 1*2,2*3,3*4,4*5,.则第一百个数是1/(100*101)=1/10100原式=1/2+1/6+1/12+/20_.1/10100=1/(1*2)+1/(2*3）+1/（3*4）+1/（4*5）+.1/（100*101）=(1-1/2)+(1/2-1/3)+(1/3-1/4）+（1/4-1/5）+.+（1/100-1/101...