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Basics of Geometry
Basics of Geometry 1.4
Let’s talk about
Angles
What we will learn
Basics of Geometry
What is an angle made up of and how do we refer
to each part of it?
How do you identify and classify the different types
of angles?
What is an angle bisector?
These questions will be answered by the end of short
this presentation.
Are you ready?!?!?!?!
Basics of Geometry
Remember Rays from yesterday…?
Let’s look at a ray:
A is called the initial
point
A
B
Ray AB extends in
one direction
without end.
Symbolized by
AB
The initial point is
always the first
letter in naming a
ray. Notice the
difference in
symbols from both
a line and segment.
Basics of Geometry
Angles
Well rays are important because they help us define something very
important in geometry…Angles!
An angle consists of two different rays that have the same initial
point. The rays are sides of the angles. The initial point is called the
vertex.
Notation: We denote an angle with
vertex
B
sides
A
C
three points and  symbol. The
middle point is always the vertex.
We can also name the angle with
just the vertex point. This angle can
be denoted as:
BAC , CAB, or A
Classifying Angles
Basics of Geometry
Angles are classified as acute, right, obtuse, and straight,
according to their measures. Angles have measures greater
than 0° and less or equal to 180°.
A
A
A
Acute angle
Right angle
Obtuse angle
Straight angle
0°< m  A < 90°
m  A = 90°
90°< m  A < 180°
m  A = 180°
A
Basics of Geometry
Angle Bisectors
An angle bisector is a ray that divides an angle into two
angles that both have the same measure.
B
A
C
Basics of Geometry
Something to think about…
You have just finished the second section in Geometry!
Like the first section, this too is a very important section
because it lays more of the foundation for the rest of the year! Much
of the vocabulary you will encounter in this course will have its
foundation in the ideas presented in this lesson as well as
yesterdays.
What is an angle made up of? Can you name the four different
types of angles? Do you know the difference between all of them?
Can you calculate and sketch the bisector of a provided angle?
The classwork and homework to come will help you in
developing a better understanding of these concepts!
Basics of Geometry
Quick Quiz !!!!
Use the diagram below to answer the following questions.
S
a. Name the type of angle.
Acute
b. Name the vertex.
R
c. Name the sides of the angle.
RT and RS
d. Name the angle three different ways.
SRT , TRS , or R
R
T