A rectangle has four right angles and two pairs of equal sides. Rectangles are four-sided polygons known as quadrilaterals. Other types of quadrilaterals are the square, rhombus, trapezoid, parallelogram and kite.
Polygons are two-dimensional shapes comprised of straight lines that are connected to each other. The name "polygon" comes from the Greek language and means "many angles." Polygons that have equal angles and sides are called "regular polygons." Those that do not have equal angles and sides are irregular. Examples of common polygons include the triangle, which has three sides; pentagon, which has five sides; hexagon, which has six sides; and octagon, which has eight sides. Polygons can have an infinite number of sides; for example, a megagon is a polygon with 1,000,000 sides.
Quadrilaterals have four sides and four interior angles which total 360 degrees. Each sub-type of quadrilateral has special properties that can differentiate it from the others:
- Rectangle: four right 90-degree angles and two pairs of parallel equal sides
- Square: four right angles and four equal parallel sides
- Parallelogram: two pairs of sides that are parallel to each other
- Rhombus: two pairs of sides that are parallel and equal
- Trapezoid: one pair of sides that are parallel
- Kite: two adjacent and equal sides
These types can be grouped into three main types of quadrilaterals: general, parallelogram and trapezoid. A rectangle and a rhombus are also parallelograms because they have two pairs of sides that are parallel. A square is also a rectangle because it has four right angles and is a parallelogram because it has two pairs of parallel sides.