1/2+1/（2*3）+1/（3*4）+1/（4*5）------1/（98*99）+1/（99*100）=1/2+1/2-1/3+1/3-1/4+1/4-1/5------------+1/98-1/99+1/99-1/100=1/2+1/2+1/100=1+1/100