basic_angle_properties-class 4 and explanations.ppt

Notes on Angles and their properties

1. Angles and Properties

2. Definition
An Angle: – Is made when two lines meet
at a common end point.
The amount of turning needed to make an
Angle is given in Degree’s
Angle is 35
o

3. Angle Types
Acute Angles are
between 0
o
to 90
o
Obtuse Angles are
between 90
o
to180
o
Reflex Angles
are over 180
o
A Right Angle
equals 90
o

4. Angle Names
P
Q R
The angle shown is called either
1) Angle RQ
ˆ
P
2) Angle PQ
ˆ
R
OR
3) Angle Q
ˆ
OR
Note: The middle letter is at the corner or Vertex
of the angle.

5. Look at each of these angles.
Decide if each is A acute, O obtuse or R right-angled.
1
2
3
4
5
6
7
8
Practice
A
O
R
A
R
O
A A

6. Practice
Use the letters to name these angles
1
P
T
R
2
C
B
D
RPT
^
DB
ˆ
C

7. 1
2 3
4 5 6
7 8 9
Acute Obtuse Acute
Reflex
Right
Obtuse
Acute Reflex
Obtuse

8. Measuring Angles

9. What do we use to help us?
A protractor
Here is a standard protractor like you use
in the classroom.

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

11. Look for the upside down ‘T’ in the middle
of the straight line on your protractor.
This needs to be exactly on the corner or
vertex of your angle.

12. We need to remember.....
It doesn’t
matter which
way round the
angle is, you
ALWAYS need
to line the upside
down ‘T’ to the vertex
of the angle.

13. Read from the 0°, and follow the inner set of numbers.

14. Once you reach 30° you need to be
careful!!!
You then need to look at the 1° markings on the
outer set of numbers.

15. What does it measure?
This angle measures 35°.

16. 1
2
Using a Protractor
0 on the outside so
use outside scale
0 on the inside so
use inside scale
67
o
50
o

17. Drawing Angles

18. Step One

19. Step Two
Put 3 dots

20. Step Three
Move the Protractor

21. Step Four
Get a ruler

22. Step Five
Draw a line along the bottom

23. Step SixDraw a line along the side

24. Step Seven
Draw a curved arc between the lines

25. Angles Properties
Some angles can be worked out without measuring
1)Angles on a straight line add up to 180
o

ab a + b = 180
o

E.G
a50
o
a + 50
o
= 180
o
a = 130
o

26. 2)Angles around a point add up to 360
o

a
b
a + b + c = 360
o

E.G
a + 90 + 120
o
= 360
o
a = 150
o


c
a
90
120
3)Vertically opposite Angles are equal
a b
a
o
= b
o

E.G
a 80
o
a = 80
o