Angles 7 for Mathlethes PDF presentation

To improve your skills in solving math problems. This presentation can help you to increase your knowledge in mathematics to become the best Mathlethe in your school!
You know, Knowledge is powerful!
We have a quote by Nelson Mandela that, "Education is the most powerful weapon which you can use to change the world", that is very true!

2. What is an angle?

Two
rays
that share the same endpoint form an
angle
. The point where the rays intersect is
called the
vertex
of the angle. The two rays are
called the
sides
of the angle.
D
E
F

3. 
Here are some examples
of
angles

4. 
We can identify an angle by using a point on
each
ray
and the
vertex
. The angle below may
be identified as

∠
ABC or
∠
CBA or
∠
B.
The
vertex point
is always in the middle.

5. D
E
F
Naming Angle
s
B
A
G

6. Measuring Angles
We measure the size of an angle using degrees.
Here are some examples of angles an
d
their degree measurements.

7. Two angles that have the same measure are called congruent
angles.
A
B
C
30
0
D
E
F
30
0
D
E
F
30
0
Congruent Angles

8. Protractor
A device used to measure angles.

9. Reading a Protractor
Which side of a protractor scale do you use?
•
The easiest way to decide which scale to use is to
look at the
angle you're measuring
.
•
If it is
greater than
a right angle (more than ninety degrees)
then use the scale that has numbers
greater than 90
.
•
If the angle is
less than
a right angle (measures less than 90
degrees), use the scale which has numbers
less than 90
.
•
Of course you have to line up the protractor correctly with
the center point on the vertex of the angle and one of the
rays of the angle coincide with the line on the protractor.

10. Measuring, calculating and
drawing angles...
Our learning objectives today
To use a protractor to:
a)
measure acute and obtuse angles to the nearest
degree.
b)
draw acute and obtuse angles to the nearest
degree.
To calculate angles on a straight line.

11. What do we use to help us
measure angles
?
A protractor
These are standard protractors.

12. When we use a protractor, we
need to line it up correctly with
the angle.
You need to make sure the protractor is lined up correctly.
Is this ready to measure the angle?

13. Is it
right?............
it wasn
’
t!
Look for the upside down
‘
T
’
in the
middle of the straight line on your
protractor.
In this protractor look for
the hole in the center.
These spots need to be exactly on the
vertex of your angle.

14. We also need to remember to
line up the base
One side of the angle
must
be lined up
with the base of the protractor.
It doesn
’
t matter which side.

15. Kinds of Angles According to their
Measures

16. Acute Angles
An acute angle is an angle measuring between 0 and
90 degrees.
Examples:

17. Obtuse Angles
An obtuse angle is an angle measuring between 90 and
180 degrees.
Example:

18. Right Angles
A right angle is an angle measuring
exactly
90 degrees.
Examples:

19. Straight Angle

A
straight angle
is
an angle measuring
exactly
180
degrees.

20. A
perigon
(or a
revolution
) is an
angle that equals exactly 360
º
.

21. Reflex Angle
A
reflex angle
is
an angle which measures
greater than 180
º
and less than 360
º
.

22. Now, we will use a protractor to measure the reflex
angle
PQR
.
Measuring Reflex Angles
To measure the reflex
angle
PQR
, extend the
arm
PQ
to
A
to form
angle
PQA
which is a
straight angle.

Then
measure the size of the
angle
AQR
and add
180
º
.