The golden gnomon is the obtuse isosceles triangle whose ratio of side to base lengths is given by 
, where 
is the golden ratio. Such
a triangle has angles of 
-
-
and can be constructed from a regular pentagon
as illustrated above in red. The corresponding 36-72-72 triangle with side-to-base
ratio 
is a golden triangle.
Golden triangles and gnomons can be dissected into smaller triangles that are golden gnomons and golden triangles (Livio 2003, p. 79).
Golden gnomons also occur as faces of golden tetrahedra (Ogievetsky and Papadopolos 2001).
