原式=1-1/2+1/2-1/3+...+1/99-1/100=1-1/100=99/100
=1-1/2+1/2-1/3+1/3-1/4+……+1/99-1/100=1-1/100=99/100 (1/(1*2)=1-1/2,1/(2*3)=1/2-1/3,……)