]]>http://www.mathisfunforum.com/profile.php?id=676942016-04-01T16:36:02Zhttp://www.mathisfunforum.com/viewtopic.php?pid=378597#p378597 I want to prove the formula of regular icosahedron's volume. The reference says that the volume is . For this, I need to split the icosahedron to 20 triangular pyramid with the same size. I assumed that the base area is and the pyramid's height is (I assumed that the pyramid's height should be equal the distance from midpoints of A'B' to the center point of pentagon A'B'C'D'E'. However, no matter how hard I tried and changed the form, I was unable to reach the form . Is the pyramid's height not equal the distance from midpoints of A'B' to the center point of pentagon A'B'C'D'E'? If so, how to determine their distance?]]>http://www.mathisfunforum.com/profile.php?id=2120312016-03-24T03:41:32Zhttp://www.mathisfunforum.com/viewtopic.php?pid=378218#p378218