Math Is Fun Forum

jesseherring

Member

Registered: 2011-07-26

Posts: 19

calculating dodecadodecahedron face angles

Wondering if anybody could show me how to calculate the face angles of the dodecahedron.  I recently got a copy of Mathematical Models and it has a table with some of the face angles calculated.  However it does not show how they got the angles.  Also does anybody know what a re-entrant angle is?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,158

Re: calculating dodecadodecahedron face angles

hi jesseherring,

See

http://en.wikipedia.org/wiki/Dodecahedron

You should be able to repeat the vector method I used for the icosahedron.

(i)  Identify which co-ordinates (section 3 on that page) are which.

(ii) Choose suitable points to get the vectors for a line of symmetry for two touching pentagons.

(iii) Use the dot product formula for the angle between the faces.

Post back if you want help with that.

Bob

Last edited by Bob (2011-08-18 20:59:32)

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob