Angles

Angles
BTESSSBAT: measure angles, identify angles, find the internal and external angles of regular polygons and use angle theorems to solve problems

Key words
acute
obtuse
rotation
reflex
internal
external
theorem
opposite
parallel
corresponding
alternate
supplementary

Angle B or angle ABC or angle CBA
A
C
Which is the largest angle?
B
G
B
D
F
E
I
E
H
H

Types of angles
Right angle
acute
90°
obtuse
180°
reflex

External angle
Internal angle

360°
540°
720°
1080°

360°
540°
180° in a triangle:
720°
1080°

360°
÷ 4
540°
÷ 5
90°
108°
720°
÷ 6
1080°
÷ 8
135°
120°

90°
72°
60°
45°

Now try these
1. A regular dodecagon has 12 sides. Find its internal angle.
2. A regular polygon has an external angle of 36° - how many sides does it have?
What is its internal angle?

Angle theorems
A theorem is a law that is always true.
360°
Angles at a point add up to
87°
55°
133°
85°

Angles on a straight line add up to
180°
85°
35°
60°

X- angles: opposite angles are equal
110°
70°
70°
110°

X- angles: opposite angles are equal
100°
In fact we only need to know one angle:
80°
80°
100°

Now try these

Angles using parallel lines
F angles: Corresponding angles (a and b) are equal

Z angles: alternate angles (c and d) are equal

Supplementary angles (a and c) add up to 180°

Now try these

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Angles

by Steve Bishop on Nov 27, 2009

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Angles — Presentation Transcript