triangle .. ^^
it is a trigon or as most people call it triangle
A polygon, but only if it has no curves.
This is formed from the ancient Greek words for 20 and 3. It is an Icosikaitrigon
heptagon
Dekagon.
circle
A 2-dimensional figure of 5 sides is a PENTAGON. A 3-dimensional solid of 5 faces is a 'PENTAHEDRON'
It's called an internally contradictory definition. "Quadrilateral" means a figure with four sides. A figure with no sides is not a quadrilateral.
A polygon.
A quadrilateral.
An octagon.
A decagon.