Learn about the properties of trapezoids including relationships among opposite sides, opposite angles, adjacent angles, diagonals and angles formed by diagonals.

**Trapezoid:** A quadrilateral with one and only one pair of parallel lines.

A trapezoid is not a parallelogram because only one pair of lines is parallel, while the other is not.

Opposite sides are not necessarily congruent.

The two parallel sides are known as the bases. The two bases will never be congruent. The two other sides are known as the legs. They may or may not be congruent.

When diagonals are drawn, nothing special happens as far as line segments go. Since they are drawn through parallel sides, we have that alternate interior angles are congruent. Vertical angles are congruent where the diagonals intersect. This gives us two similar triangles.