Download Sum of interior angles

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PLT Skills
LESSON OBJECTIVES
Always aim
high!
We are learning to:
- Finding connections between different words.
(Which PLT skills?)
- Accurately find missing angles in polygons.
(Grades D-C)
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our journey?
AUTHOR
www.mistrymaths.co.uk
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BRAIN IN GEAR
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EXAMPLE
DITDIONA can be rearranged to make ADDITION
TASK
Work out the following Mathematical anagrams:
LONYGOP
Polygon
SEEDG
Edges
TSERVICE
Vertices
EXTENSION
Develop your own Mathematical anagrams as above as a
creative thinker.
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STARTER
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TASK
Equilateral
Isosceles
1)
2)
50°
4)
3)
30°
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20°
45°
Find the value
of each angle
180° - 50° - 45°
85°
180° - 90° - 30° 180°- 20° 160°
160°
60°
60°
2
80°
EXTENSION
Work out the following without a calculator:
1) 180 x 3
= 540
2) 180 x 5
= 900
3) 180 x 6
= 1080
4) 180 x 8
= 1440
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ANGLES IN POLYGONS
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INTRODUCTION
NON-POLYGONS
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POLYGONS
QUESTION
WHAT IS A POLYGON?
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ANGLES IN POLYGONS
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INTRODUCTION
5 x 180°
8 x 180°
900°
6 x 180°
1440° 9 x 180°
7 x 180°
1260°
1620° 10 x 180°
1800°
1080°
What is the connection?
Sum of interior angles = (number of sides – 2) x 180°
Always two less triangles than sides
Sum of angles in a triangle
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ANGLES IN POLYGONS
LEARN
OFF BY
HEART
EXAMPLES
1)
Self
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2)
95°
120°
155°
110°
80°
95°
120°
Pentagon (5 sides)
105°
Hexagon (6 sides)
Sum of interior angles = (number of sides – 2) x 180° Sum of interior angles = (number of sides – 2) x 180°
Sum of interior angles = ( 5 – 2 ) x 180°
Sum of interior angles = 3 x 180°
Sum of interior angles = 540°
- 90° - 155°- 95°- 80°
Sum of interior angles = ( 6 – 2 ) x 180°
Sum of interior angles = 4 x 180°
Sum of interior angles = 720°
-120°- 110°-120°- 95°- 105°
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PLT Skills ANGLES IN POLYGONS
TASK (GRADE D)
1)
110°
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4)
3)
2)
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245°
100°
60°
5)
7)
6)
145°
9)
8)
275°
85°
10)
30°
12)
11)
135°
50°
280°
85°
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ANGLES IN POLYGONS
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EXTENSION (GRADE C)
Which regular polygons have:
a) a total sum of 2340°
15 sides
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b) a total sum of 5400° c) a total sum of 17820°
101 sides
32 sides
d) interior angles of 156° e) interior angles of 150° f) interior angles of 170°
15 sides
36 sides
12 sides
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ANGLES IN POLYGONS
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MINI-PLENARY
Why is this building famous in America? What is the value of each interior angle?
PENTAGON
United States Defence Headquarters
Sum of interior angles = (number of sides – 2) x 180°
Sum of interior angles = ( 5 – 2 ) x 180°
Sum of interior angles = 3 x 180°
Sum of interior angles = 540°
540°
Each interior angle =
5
Each interior angle = 108°
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DISCOVERY
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LINK BACK TO OBJECTIVES
- Accurately find missing angles in polygons.
What grade
are we
working at?
PLENARY ACTIVITY
EXAM QUESTION (GRADE C)
2x
3x + 5
140°
3x
Sum of interior = (n – 2) × 180
= (5 – 2) × 180
= 3 × 180
= 540°
75°
Calculate the value of x
2x + 3x + 5 + 3x + 75 + 140 = 540°
8x + 220 = 540°
8x
= 320°
x
= 40°
What have you learnt?
Draw your brain
In your brain, write or draw everything you can remember about finding
missing angles in polygons. It can be a skill or a reflection, or something
else that might be prominent in your brain.
Where are we
in our
journey?
What grade
are we
working at?
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Plenary Activity
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I fully
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EBI (Even Better If)
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