=(1/2)*(1-1/3)+(1/2)*(1/3-1/5)+……+(1/2)*(1/13-1/15)=(1/2)*(1-1/3+1/3-1/5+……+1/13-1/15)=(1/2)*(1-1/15)=7/15
1/1*3+1/3*5+1/5*7+...+1/13*15=(1/2)(1-1/3+1/3-1/5+1/5-1/7+...+1/13-1/15)=(1/2)(1-1/15)=7/15
