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# Angles in Triangles

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by

## Mr Mattock

on 26 November 2016

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#### Transcript of Angles in Triangles

Angles in Triangles
Starter
Find the missing angles:
L.O. - To demonstrate the sum of angles in a triangle and calculate missing angles in triangle
57
o
a
145
o
155
o
b
b
57
a
b
o
Starter
Find the missing angles:
57
o
123
145
o
155
o
30
30
57
57
o
o
o
o
o
Main Activity
Complete the Angles in triangles sheet
Example
Key
Examples

Activities
Activity

c
123
123
o
o
Angles in triangles
Cut out a triangle. Mark the angle and put a dot in each corner and tear off the corners.
Can you arrange the three pieces so that that dots are together? What shape do you get?
Angles in triangles
Cut out a triangle. Put a dot in each corner and tear off the corners.
The three pieces form a straight line.
Angles on a straight line add up to 180
o
68
62
o
o
Find the value of angle ABC
A
B
C
P
Q
R
42
o
Find the values of the angles QPR and PRQ.
Example
68
62
o
o
Find the value of angle ABC
A
B
C
P
Q
R
42
o
Find the values of the angles QPR and PRQ.
62 + 68 + ABC = 180
130 + ABC = 180
ABC = 180 - 130 = 50
o
o
o
o
o
o
o
o
QPR = 42
42 + 42 + PRQ = 180
84 + PRQ = 180
PRQ = 180 - 84 = 96
o
o
o
o
o
o
o
o
o
Worked
Example

Worked
Example

Main Activity
Complete the Angles in triangles sheet
a = 60 b = 50 c = 45 d = 70

e = 43 f = 43 g = 35 h = 46

i = 60 j = 39 k = 45 l = 71
o
o
o
o
o
o
o
o
o
o
o
o
Plenary
Plenary
45 + 55 + ACB = 180

100 + ACB = 180

ACB = 80

x + ACB = 180

x + 80 = 180

x = 180 - 80 = 100
o
o
o
o
o
o
o
o
o
o
o
o
Main Activity
The large triangle is equilateral. All other triangles are isosceles.
How many angles can you work out in the picture?
Full transcript