Geometry – Polygons & Angle Vocabulary

Key vocabulary terms covering polygons, angle measurement tools, and the various classifications and relationships of angles presented in the lecture notes.

Angle

The shape formed by two rays meeting at a common endpoint.

Ray

A part of a line that starts at a point (endpoint) and extends infinitely in one direction.

Protractor

An instrument used to measure angles in degrees.

Degree (°)

The unit of measurement for angles; a full rotation equals 360 degrees.

Right Angle

An angle that measures exactly 90°.

Straight Angle

An angle that measures exactly 180°.

Acute Angle

An angle that measures less than 90°.

Obtuse Angle

An angle that measures more than 90° but less than 180°.

Reflex Angle

An angle that measures more than 180° but less than 360°.

Adjacent Angles

Two angles that share a common side and vertex and lie next to each other.

Vertical Angles

Opposite angles formed when two lines intersect; the opposite angles are equal.

Complementary Angles

A pair of angles whose measures add up to 90°.

Supplementary Angles

A pair of angles whose measures add up to 180°.

Conjugate Angles

A pair of angles whose measures add up to 360°.

Square

A quadrilateral with four equal sides and four right angles.

Rhombus

A quadrilateral with four equal sides; opposite sides are parallel and opposite angles are equal.

Triangle

A polygon with three sides and three angles.

Pentagon

A polygon with five sides and five angles.

Hexagon

A polygon with six sides and six angles.

Heptagon

A polygon with seven sides and seven angles.