Quadrilaterals and Polygons: Parallelograms

Parallelograms: Sides

The first property of parallelograms is that opposite sides are parallel. This leads to the second property of parallelograms, which is that opposite sides are congruent.


As we stated in the definition, opposite sides of a parallelogram are parallel. This is the first, and most basic property of parallelograms. This leads to the second property of parallelograms, which is that opposite sides are congruent.


Take a look at this figure:


Parallelogram ABCD


If we know that this is a parallelogram, we know the following:

  • Side AB is parallel to side DC (line segment AB is parallel to line segment DC)
  • Side AD is parallel to side BC (line segment AD is parallel to line segment BC)
  • Side AB is congruent to side DC (line segment AB is congruent to line segment DC)
  • Side AD is congruent to side BC (line segment AD is congruent to line segment BC)