A two-dimensional figure is a figure without thickness; it is flat.
A polygon is a two-dimensional figure
made up of non-overlapping, straight line segments.
The point where two line segments meet is a vertex, or corner.
triangle | quadrilateral | pentagon | hexagon | heptagon | octagon |
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3 sides 3 vertices | 4 sides 4 vertices | 5 sides 5 vertices | 6 sides 6 vertices | 7 sides 7 vertices | 8 sides 8 vertices |