section 1-4: measuring angles
DESCRIPTION
Section 1-4: Measuring Angles. Objective: Find the measurement of angles using the Angle Addition Postulate. Vocabulary. Angle. Formed by two rays with the same endpoint. Rays. Vertex (endpoint). Naming Angles. 1. Name the Rays of the angle:. - PowerPoint PPT PresentationTRANSCRIPT
Section 1-4: Measuring Angles
Objective: Find the measurement of angles using the Angle Addition Postulate
AngleFormed by two rays with the same endpoint.
Rays
Vertex(endpoint)
Naming Angles
Name the Rays of the angle:
What is the vertex of the angle? Vertex is B
1
Different ways to name the angle: • Name by vertex:• Name by 3 points (vertex in middle):• Name by a number:
Geometry is used to construct roofs. Use the diagram below to answer the following questions.
F
G
H
1 2
What is the vertex of the large angle?
Name all the angles in the diagram using both letters & numbers.
Name the Rays of the angle:
The vertex is G
I
Protractor PostulateFor every angle, there corresponds a number between 0 and 180º. This number is called the measure of the angle and is written in degrees.
Postulate 1-7
Measuring Angles and the Protractor Postulate
Four Different Classifications of Angles
Right Angle Straight Angle
Acute Angle Obtuse Angle
Using a Protractor to Measure Angles
1. Place the vertex at zero on the protractor2. Align one ray with the bottom edge of the protractor3. Read measurement (in degrees) on protractor4. Caution:
Pay attention to the numbersEnsure answer makes sense
What type of angle is represented in the diagram?
Angle Addition PostulatePostulate 1-8
Angle Addition Postulate
If the mDEG = 145º , find the mGEF.
D E F
G
145º + _____ = 18035
AXB and BXD form linear pairs and are adjacent angles
Name the adjacent angles? Are they a linear pair?
Use the Angle Addition Postulate to solve.
m 1 + m 2 = m ABC Angle Addition Postulate.
42 + m 2 = 88 Substitute 42 for m 1 and 88 for m ABC.
m 2 = 46 Subtract 42 from each side.
Suppose that m 1 = 42 and m ABC = 88. Find m 2.
What postulate do you use to solve the problem?