A twenty sided, 2D figure is called an icosagon.
The vertex of an angle
A two-dimensional figure is a polygon. The eight sides means that it uses the prefix octa- (meaning eight) to form the name octagon.
A regular hexagon.
Quadrilateral is the name fr a geometric figure with 4 sides.
The correct name would be a "tetradecagon"
It is called a circle.A circle is an ellipse with zero eccentricity.Incidentally, you probably meant "geometric figure".
It is called a Tetrahedron.
It is called a heptagon or a septagon,
A 5-sided figure is called a "Pentagon".
a 12 sided figure is called a dodecagon
I think a circle
For a Polygon, "Poly" means "many" or "a number of"; "gon", roughly means "angles". So a poloygon is a figure with a number of angles between its sides. . If the number of sides is definite then "poly" is replaced by a word meaning that number.