Measuring AnglesGeometryMrs. King
Unit 1, Lesson 5
Definition
Angle: formed by two rays with a common endpoint (“vertex”).
C
A
B
Name the angle below in four ways.
*The name can be the vertex of the angle: G.
The name can be a point on one side, the vertex, and a point on the other side of the angle: AGC, CGA.
The name can be the number inside of the angle: 3.
Practice
Types of Angles
1. AcuteLess than 90°
2. RightExactly 90°
3. ObtuseGreater than 90°,
but less than 180°
Types of Angles
4. StraightExactly 180°
5. ReflexGreater than
180 but less than 360
Definition
Congruent Angles: angles with the same measure
Angle Addition Postulate
1-8: If point B is in the interior of AOC, then mAOB + mBOC = mAOC
O C
BA
PracticemHAT = 50 and mHAM = 125. What is the mMAT?
A H
TM
m 1 + m 2 = m ABC
42 + m 2 = 88
m 2 = 46
Suppose that m 1 = 42 and m ABC = 88. Find m 2.
Practice
Angle Pairs
1. Vertical Angles: two angles whose sides are opposite rays
1 and 3 are vertical angles, and 2 and 4 are vertical angles.
2. Adjacent Angles: two coplanar angles with a common side, a common vertex, and no common interior points.
1 and 2 are adjacent angles
Angle Pairs
3. Complementary Angles: two angles whose measures have a sum of 90.
4. Supplementary Angles: Two angles whose measures have a sum of 180.
In the diagram, these angles are supplementary:1 and 2,
2 and 3,
3 and 4,
and 4 and 1.
Homework
Measuring Angles in Student Practice Packet(Page 6, #1-13)