由(1-1/4)(1-1/9)(1-1/16)(1-1/25)。。。(1-1/2025)=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)。。。。(1-1/45)(1+1/45)=(1-1/2)(1-1/3)(1-1/4).。。。(1-1/45)(1+1/2)(1+1/3)(1+1/4)。。。(1+1/45)=1/2×2/3×3/4×。。。×44/45×3/2×4/3×5/4×。。。×46/45=1/45×2/46=23/45.