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Quadrilaterals

A quadrilateral is a plane figure bounded by four straight sides.

Convex quadrilateral ABCD

This quadrilateral is called a convex quadrilateral because none of its four interior angles is a reflex angle.

Non-convex quadrilateral ABCD

This quadrilateral is called a non-convex quadrilateral because one of its interior angles is a reflex angle.

A quadrilateral has two diagonals that join opposite vertices.

Convex quadrilateral ABCD with dashed diagonals AC and BD

Both diagonals of a convex quadrilateral are inside the quadrilateral.

Non-convex quadrilateral ABCD with dashed diagonals AC and BD

One of the diagonals of a non-convex quadrilateral is outside the quadrilateral.