1*3*5分之1 +3*5*7分之1+5*7*9分之1•••••••+11*13*15分之1=1/4[1/(1×3)-1/(3×5)+1/(3×5)-1/(5×7)+...+1/(11×13)-1/(13×15)]=1/4[1/(1×3)-1/(13×15)]=1/4×64/195...