Angles
Angles are formed by two rays that have a common endpoint. A B C Notice ray AB and ray BC have a common endpoint, point B. Point B is called the vertex of the angle and ray BA and ray BC are called the sides.
A B C ∠B ∠ 1 Notice that when you name an angle ∠ ABCwith three letters that the vertex letter is always in the middle. ∠ CBA 1 This angle can be named in four different ways.
Angles are measured in units called degrees. In order to measure angles, we use a tool called a protractor.
View this clip about how to measure angles. Click here to view video
The Acute angle measures between 0 and 90 degrees. The Right angle measures exactly 90 degrees. The Obtuse angle measures between 90 and 180 degrees. The Straight angle measures exactly 180.
Measured in degrees Acute angleRight angleObtuse angle Straight angle
The angle addition postulate states: For any angle PQR, if A is in the interior of ∠PQR, then m∠PQA + m∠AQR = ∠PQR P Q A R
When working with angles, sometimes we compare angles. These are adjacent angles – ones that share a vertex and a common side but no interior points. Angle 1 and Angle 2 are said to be adjacent 1 2
Linear Pair Angles Linear Pair angles are adjacent angles that have their non-common side laying in a straight line. ∠ MNO and ∠ MNP are called linear pair angles. M N O P
Two angles that when added together equal 90 degrees. ∠ABC and ∠CBD are complementary angles. Complementary angles Two angles that when added together equal 180 degrees. ∠WYX and ∠ XYZ are supplementary angles. Supplementary angles A C B D W X YZ
Congruent angles are angles of equal measure. A special pair of angles that are congruent are the vertical angles. ∠1 and ∠3 are vertical angles and are equal in measure. ∠2 and ∠4 are vertical angles and are equal in measure
Perpendicular lines are two intersecting straight lines that form right angles. MN ⊥ OP, thus forming four right angles. M N O P