Lesson 5 Notes

A polygon is a close figure consisting of segments that intersect only at their endpoints.  The endpoints are called vertices.

A convex polygon is a polygon in which any line segment connecting any two interior points of the polygon is in the interior of the polygon.  If a polygon is not convex, it is concave.

For the rest of the unit, we will use the word "polygon" to mean "convex polygon."

A polygon with three sides is a triangle.

A polygon with four sides is a quadrilateral.

A polygon with five sides is a pentagon.

A polygon with six sides is a hexagon.

A polygon with seven sides is a heptagon.

A polygon with eight sides is a octagon.

A polygon with nine sides is a nonagon.

A polygon with ten sides is a decagon.

A polygon with twelve sides is a dodecagon.

Regular polygons are both equilateral and equiangular.

A parallelogram is a quadrilateral with two pairs of parallel sides.