Transcript Document

A 180o Protractor
Outside scale from
0o to 180o going in a
clockwise direction.
Inside scale from
0o to 180o going in an
anti-clockwise direction.
You need to be able to measure an angle to the nearest
degree. To help you do this you should always:
1. Look directly down onto the cross point. (this avoids parallax
errors)
2. Always use the protractor in a horizontal manner as shown
below.

1
Measuring
Angles with a
180o Protractor
50o
2
0 on the inside so
use inside scale
67o
0 on the outside so
use outside scale
3
Measuring
Angles with a
180o Protractor
120o
4
135o
0 on the outside so
use outside scale
0 on the inside so
use inside scale
What’s in the box ?
Measuring
Angles with a
180o Protractor
1
80o
2
0 on the inside so
use inside scale
55o
0 on the outside so
use outside scale
3
Measuring
Angles with a
180o Protractor
150o
4
0 on the inside so
use inside scale
165o
0 on the outside so
use outside scale
Measure each angle in the shapes below.
Answer on your worksheet.
2
1
4
5
3
6
Measure each angle in the shapes below.
900
1
2
680
900
900
680
900
Rectangle 3600
4
1070
730
460
1120
Trapezium 3600
5
480
900
Triangle 1800
6
1180
1010
1070
Parallelogram 3600
670
670
1120
420
730
3
Triangle 1800
1100
1010
1100
Pentagon 5400
1
3
5
Estimating Angles
2
4
6
Naming Angles
Angles are named using the three letters that form
them.
The middle of the three letters is the vertex of the
angle (pointy bit)
D
DEF or DÊF or FED or FÊ D
E
F
Measuring Angles
 AOB = 27o
AOC = 122°
C
B
A
O
Types of angle
Acute angle
(less than 90°)
Right Angle
(90°)
Obtuse angle
(between 90°
and 180°)
Straight angle
(180°)
Reflex angle
(more than 180°)
What’s in the box 2 ?
A
1
C
D
What type of angle is this?
OBTUSE
What is the name of the angle
2
P
Q
marked with *?
PQS or SQP
*
R
marked with *?
ACB or BCA
*
B
What is the name of the angle
S
What type of angle is this?
ACUTE
Complementary angles add up to 90°
So the complement of 40° is 50°
CO
Supplementary angles add up to 180°
The supplement of 40° is 140°
1S0
Angle Reasons
130°
x
x = 50°
Adjacent angles on a straight
line sum to 180°
70°
x
x
80° 120°
110°
x = 70°
Vertically opposite angles are equal
x = 50°
Angles at a point sum to 360°
x
x = 60°
Angles in a triangle sum to 180°
50°
70°
x = 50°
Base angles of an isosceles
triangle are equal
50°
x
x = 60°
Each angle in an equilateral
triangle is 60°
x
Angles on Parallel Lines
transversal






110°
x
50°




x
110°
x
x = 110°
Corresponding angles on
parallel lines are equal
x = 50°
Alternate angles on parallel
lines are equal
x = 70°
Co-interior angles on parallel
lines sum to 180° EXTENSION
Types of Triangles (according to sides)
Scalene - no equal sides
Isosceles - 2 equal sides
Equilateral - 3 equal sides
Types of Triangles (according to angles)
Acute angled triangle - all angles equal
Right angled triangle - one 90° angle
Obtuse angled triangle - one angle  90°
What’s in the box 3 ?
125o
co
ao
100o
bo
35o
To find c you must use the new fact
that in all triangles the three angles add up to 180o
a=
55
b=
125
c=
65