上面那道简便计算怎么做裂项法1/1×3+1/3×5+1/5×7+1/7×9+1/9×11=1/2×（1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11）=1/2×（1-1/11）=1/2×10/11=5/11
