Key Concepts: Angle Measure

Angles

An Angle is formed by two rays with a common endpoint called the vertex. The rays are called the sides of the Angle. Angles are measured in degrees (°).

Types of Angles

• Acute Angle: An Angle measuring between 0° and 90°.
• Right Angle: An Angle measuring exactly 90°.
• Obtuse Angle: An Angle measuring between 90° and 180°.
• Straight Angle: An Angle measuring exactly 180°.

Angle Addition Postulate

If Point D is in the interior of ∠ABC, then m∠ABD + m∠DBC = m∠ABC.

Congruent Angles

Two angles are congruent if they have the same measure. Notation: ∠A ≅ ∠B.

Angle Bisector

An Angle bisector is a ray that divides an Angle into two congruent angles.