A lot of things, but the answer that comes to my mind is: they are all convex, planar, simple closed curves.
Most shapes. For example, triangles, pentagons, hexagons, heptagons, 8-gons, 9-gons etc; circles, ellipses, ovals and other random meandering curves.
The number of hexagons that can be formed from two triangles depends on how the triangles are arranged and whether you are referring to overlapping shapes or distinct hexagons made from their combination. If you are asking about a specific geometric arrangement, please provide details. In a general sense, two triangles do not inherently contain any hexagons.
Hexagons are only combined triangles and would demonstrate the same functions and relationships as triangles. Geometry is the study of all shapes. This includes hexagons. Trigonometry developed much later than geometry for applying the study of triangles to practical application.
Only when they are equilateral triangles and regular hexagons that both will have sides of equal lengths.
Triangles, squares and hexagons.
The reguar polygons are triangles, quadrilaterals and hexagons.
Equilateral triangles, squares, and hexagons.
Triangles, Squares and Hexagons always tessellate.
Quadrilaterals, pentagons, triangles, octagons, hexagons, decagons.
Triangles, squares, hexagons, and octagons all tessellate
2 hexagons and six triangles
Basically, they represent 2D shapes. This question requires more information.