裂项法:2/3×5+2/5×7+2/7×9+2/9×11+……+2/97×99+2/99×101=1/3-1/5+1/5-1/7+1/7-10/9+1/9-1/11+……+1/97-1/99+1/99-1/101=1/3-1/101=98/303