1/1×3+1/3×5+1/5×7+1/7×9+1/9×11
=（1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11）÷2
=（1-1/11）÷2
=10/11÷2
=5/11我没看明白啊。可以说的详细点么？1/1×3=（1-1/3）÷21/3×5=（1/3-1/5）÷21/5×7=（1/5-1/7）÷21/7×9=（1/7-1/9）÷21/9×11=（1/9-1/11）÷2