Definition: A polygon is a closed flat figure made of three or more straight line segments that meet only at their endpoints.
What is a polygon?
A polygon is a closed shape with straight sides. The sides meet at vertices, and no sides cross. Circles are not polygons, since they have curves.
How do polygons get their names?
By the number of sides: triangle (3), quadrilateral (4), pentagon (5), hexagon (6), octagon (8).
What does regular mean?
A regular polygon has all sides equal and all angles equal, like a stop sign. An irregular polygon does not.
How do you find the area of an irregular polygon?
Split it into rectangles and triangles. Suppose an L-shape is made from a 10 by 4 rectangle and a 3 by 6 rectangle. The areas are 40 and 18, so the total is 58 square units.
What about the angle sum?
The interior angles of an n-sided polygon sum to (n – 2) x 180 degrees. A hexagon: (6 – 2) x 180 = 720 degrees.
What is a common mistake?
Calling a shape with a gap a polygon. If the figure is open, it is not closed, and so it is not a polygon.