Download Missing Angles

Geometry Terms
Point
Line
segment
A location
End Point
A straight path between the
points, called its endpoints.
Line
A straight path that goes on
forever in both directions.
Ray
A straight path that goes on
forever in one direction from
an endpoint.
Angles In Daily Life
If we look around us,
we will see angles everywhere.
Review Naming an Angle
To name an angle, we name any point on one ray, then
the vertex, and then any point on the other ray.
A
B
C
For example: ABC or CBA
We may also name this angle only by the single letter of
the vertex, for example B.
Review Types f Angles
There are four main types of angles.
Right angle
Acute angle
A
B
Obtuse angle
A
A
C
B
B
C
Straight angle
A
B
C
C
Right angle: An angle whose measure is 90 degrees.
Straight Angle
Right Angle
Acute Angle
Obtuse Angle
Examples Of Right Angle
Examples Of Obtuse Angle
Acute angle: An angle whose measure is less than 90
degrees.
Straight Angle
Right Angle
Acute Angle
Obtuse Angle
Examples Of Acute Angle
Straight angle: An angle whose measure is 180 degrees.
Straight Angle
Right Angle
Acute Angle
Obtuse Angle
Examples Of Straight Angle
Lines in a plane
What can you say about these pairs of lines?
These lines
cross, or
intersect.
These lines do
not intersect.
They are parallel.
Angles
Angles are measured in degrees.
A quarter turn
measures 90°.
90°
It is called a right
angle.
We label a right angle with a
small square called a square
corner.
Angles
A half turn measures 180°.
180°
This is a straight angle
Angles
360°
A full turn
measures 360°.
Adjacent Angles
Two angles that have a common vertex and a common ray
are called adjacent angles. “SIDE BY SIDE”
A
A
C
D
Common ray
B
D
B
Common
vertex
E
C
F
Adjacent
ABD
and DBC
ABC
and Angles
DEF arenot
adjacent
angles
Adjacent angles do not overlap each other.
More examples of adjacent angles.
80º
45º
35º
55º
130º
85º
20º
50º
Missing
Angles
Our learning objectives today
•To calculate missing angles on a straight
line, around a point and in a triangle.
What do you need to know?
Angles in a triangle add up to.................
180°
Angles on a straight line add up to.......
180°
Angles around a point add up to.............
360°
Complementary Angles
Two angles are called complementary angles if the
sum of their degree measurements equals 90
degrees.
Example:
These two angles are complementary.
These two angles can be “put" together to
form a right angle which is complementary!
Supplementary Angles
Two angles are called supplementary angles if the
sum of their degree measurements equals 180
degrees.
Example:
These two angles are supplementary.
These two angles can be “put"
together to form a straight line!
Find the missing angle.
You do not have a protractor.
Use the clues in the pictures.
1.
x
55
X=35
Find the missing angle.
You do not have a protractor.
Use the clues in the pictures.
2.
x
165
X=15
Calculate the missing
straight line angle
69°
111°
Calculate the missing
triangle angle
89°
37°
54°
Calculate the missing
straight line angle
103°
35°
42°