1/1*2=2-1/1*2=1/1*2+2/1*2=1-1/2
同理1/2*3=1/2-1/3 1/3*4=1/3-1/4.
原式=1-1/2+1/3-1/3+1/4-1/4.-1/99+1/99-1/100
=1-1/100
=99/100