这样1.2/3+2/15+2/35+2/63+2/99 =2/1*3+2/3*5+2/5*7+2/7*9+2/9*11 =1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11 =1-1/11 =10/11