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.