1/3-1/15-1/35-1/63-1/99 =1/(1*3)-1/(3*5)-1/(5*7)-1/(7*9)-1/(9*11)=1/2(1-1/3)-1/2(1/3-1/5)-1/2(1/5-1/7)-1/2(1/7-1/9)-1/2(1/9-1/11)=1/2(1-1/3-1/3+1/5-1/5+1/7-1/7+1/9-1/9+1/11)=1/2(1-1/3-1/3+1/11)=1/2(1/...