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).
