A quadrilateral is a polygon with four vertices and four sides.
Glossary Term: Definitions
A list of geometrical definitions and postulates.
The radius of a circle or a sphere is the distance of its centre to its perimeter.
Invariance of an object under reflection in a line (2D) or a plane (3D). Also known as mirror symmetry.
A polygon of which all sides have equal length.
A parallelogram with four equal sides. In a rhombus the diagonals are perpendicular and divide each other in half.
A triangle with a right angle (90 degrees).
Invariance of an object under a certain rotation.
The Side Angle Side postulate (often abbreviated as SAS) states that if two sides and the included angle of one triangle are congruent to two sides and the included angle of another triangle, then these two triangles are congruent.
A line that intersects a curve (mostly a circle) at a minimum of two distinct points.
A circle cut in half along its diameter.