A quadrilateral is a polygon characterized by:

- 4 vertices (or corners) represented by the letters A, B, C, D.
- 4 straight sides which are segments joining the vertices together: [AB], [BC], [CD], [AD].
- 2 diagonals which are segments joining 2 opposite vertices: [AC], [BD].
- 4 interior angles.

The quadrilaterals can be classified into two large families:

- the convex quadrilaterals: their diagonals cross the interior of the quadrilateral.
- the concave quadrilaterals: one of their diagonals is outside the quadrilateral. If both diagonals are outside the quadrilateral figure, the quadrilateral is known as crossed (or complex).

**Click** and **drag** the vertices of the quadrilateral.

**Click** on the ruler to take measurements.

**Click** on the question mark when it appears.