S4E20. 5维空间的球体积为啥最大？

<p style="color:#333333;font-weight:normal;font-size:16px;line-height:30px;font-family:Helvetica,Arial,sans-serif;hyphens:auto;text-align:justify;" data-flag="normal">1到5维球体积公式前的系数：</p><p style="color:#333333;font-weight:normal;font-size:16px;line-height:30px;font-family:Helvetica,Arial,sans-serif;hyphens:auto;text-align:justify;" data-flag="normal"><img data-key="0" src="http://imagev2.xmcdn.com/storages/a133-audiofreehighqps/EB/ED/GKwRIW4H6_2QAAEYnAIEHVW_.png!op_type=4&amp;device_type=ios&amp;upload_type=attachment&amp;name=mobile_large" alt="" data-origin="http://imagev2.xmcdn.com/storages/a133-audiofreehighqps/EB/ED/GKwRIW4H6_2QAAEYnAIEHVW_.png?op_type=0" data-large="http://imagev2.xmcdn.com/storages/a133-audiofreehighqps/EB/ED/GKwRIW4H6_2QAAEYnAIEHVW_.png!op_type=4&amp;device_type=ios&amp;upload_type=attachment&amp;name=mobile_large" data-large-width="750" data-large-height="542.4107142857142" data-preview="http://imagev2.xmcdn.com/storages/a133-audiofreehighqps/EB/ED/GKwRIW4H6_2Q...