Geometry: Quadrilaterals

Quadrilaterals are two-dimensional four-sided polygons on a plane. They have four internal angles. We will describe the five most common types here: parallelograms, rhombus, rectangles, squares, and trapezoids.

Parallelograms

In a parallelogram, the opposite sides are equal and the opposite angles are equal. Opposite sides are parallel.

Rhombus

A rhombus is a special case of a parallelogram with four equal sides.

Rectangles

A rectangle is a special case of a parallelogram. The opposite sides are equal and all angles are right angles (i.e. 90º).

Squares

A square is a special case of a rectangle in which the lengths of all sides are equal.

Take note that a diagonal of a square makes two 45º-45º-90º triangles with the sides of the square. Therefore, when given the length of a side, you will be able to work out the length of the diagonal. Or when given the length of the diagonal, you will be able to figure out the length of the side.

Trapezoids

A trapezoid is a four-sided polygon that has exactly two sides parallel.

l is parallel to m	p is parallel to q

The following video shows how to identify quadrilaterals given some properties.

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