14.17.5  Icosahedra: icosahedron

The icosahedron command creates regular icosahedra.

• icosahedron takes three arguments:
  A,B,C, three points.
• icosahedron(A,B,C) returns and draws the icosahedron centered at A with a vertex at B and such that the plane ABC contains one of the vertices closest to B.

Examples.

• Input:
  icosahedron([0,0,0],[0,0,5],[0,1,0])
  Output:
  
• Input:
  icosahedron([0,0,0],[0,0,sqrt(5)], [2,1,0])
  Output: