1/n^2-1=1/(n+1)(n-1)S=0.5(1-1/3+1/2-1/4+1/3-1/5+.........+1/10-1/12)=0.5*(1+1/2-1/11-1/12)=175/264
175/264 每项可以拆开来 1/3=1/2(1-1/3) 1/8=1/2(1/2-1/4)以此类推
