Trapezium

A quadrilateral with at least one pair of parallel sides. Also known as trapezoid.

Triangle proportionality theorem

In any triangle, if a line intersects two sides of the triangle and is parallel to the third, then and only then the intersecting line divides the sides proportionally.

Unit circle

A circle with radius 1.

Vector

An object that has a magnitude (length) and direction. Vector algebra is widely used in physics.

Vertex

A point where two lines, curves or edges meet.