A circle is one example of a plane figure that is not a polygon. A V is also not a polygon.
Although a polygon is usually thought of as a two-dimensional figure with at least three sides, there is nothing in the definition of a polygon that prohibits its use for the classification of a one-sided figure. A one-sided figure is known as a henagon or a monogon. A polygon, by definition, has as many vertices as it has sides, so a single-sided polygon would have to, in order to meet that criterion, curve in on itself so that the two ends of the side meet to form a vertex. In order for the polygon to not be curved, it would have to be made up of two straight lines (this figure is known as a digon). So no, a polygon cannot be a single straight line.
A polygon is a plane figure which comprises one area bounded by three or more straight line segments. A general plane figure can have curved boundaries or sides that cross each other.
cone; circle is the base
A polygon is a closed plane figure composed of several line segments that are joined together. A one hundred sided polygon is called a hectogon or a hecatontagon.
a pyramid
Such a figure is a pyramid.
A geometric figure with a polygonal base and triangular sides is called a pyramid.
It could be a pyramid.
A polygonal pyramid.
There are many but I guess that the answer that you are looking for is a pyramid.
A polygon is a 2-dimensional figure bounded by three or more straight lines. Any one of its sides may be considered a base.
a polygonal prism or a polygond
It is a polygonal pyramid.
A polygon is a many sided 2-dimensional figure, and thus could never be "solid" Alternatively, it could be "one face that is a polygon". In that case the solid could be like a pyramid that morphs into a cone or a part-sphere. The base would be the one polygon, the other face would not.
A circle is one example of a plane figure that is not a polygon. A V is also not a polygon.
Pyramid, base