Level 4/5 Booster

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Level 4/5 Booster
Lesson 8B
Triangles and Quadrilaterals
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Objectives

• To identify and use the properties of triangles
  and quadrilaterals.

Vocabulary
parallel
rotational symmetry
opposite
quadrilateral
external angle
congruent
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Name the quadrilaterals and state their
identifying properties
W/S 8.1B
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Parallelogram
Opposite sides equal
Opposite sides parallel
No lines of symmetry
Rotational symmetry order 2
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Rectangle
Opposite sides equal (and parallel)
All angles 90º
Two lines of symmetry
Rotational symmetry of order 2
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Rhombus
All sides equal
Opposite sides parallel
Two lines of symmetry
Rotational symmetry of order two
Isosceles trapezium
One pair of equal sides
One pair of parallel sides
A line of symmetry
No rotational symmetry
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Square
Trapezium
Four equal sides
One pair of opposite sides parallel
All angles 90º
No lines of symmetry
Four lines of symmetry
No rotational symmetry
Rotational symmetry of order 4
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You need W/S 8.2B
Using a 3 by 3 pinboard draw as many different
triangles as you can find.
Example
These two triangles are the same (congruent)
one is a translation of the other.
These two triangles are the same (congruent)
one is a rotation of the other.
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Here are the 8 different triangles that are
possible.
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Which of these triangles have an obtuse angle?
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Which of these triangles are isosceles?
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Which of these triangles contain a right angle?
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Conventional labelling
A
B
The marked angle is angle ADC or angle CDA.
Sometimes written as ltADC or ADC
D
ˆ
C
How would you describe the angle indicated in the
same way?
A
Estimate the size of angle BAD.
50 - 60º
B
What type of angle is angle ADC?
Obtuse
D
C
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C
AB has been extended to point D.
Angle CBD (marked) is an external angle of the
triangle.
D
A
B
Follow these instructions

• Draw a triangle and label the vertices A, B and
  C.

• Extend line BC to the point D and label point D.

• What do you know about the angles ACD and ACB?

Angles ACD and ACB are on a straight line and
therefore have a sum of 180º.
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You have two congruent right-angled triangles.
What different quadrilaterals can you make by
putting sides of equal length together?
Example
parallelogram
Using two congruent right-angled triangles what
other shapes can you make?
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Here are the quadrilaterals you can find.
Other shapes you can produce are
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Objectives

• To identify and use the properties of triangles
  and quadrilaterals.

Vocabulary
parallel
rotational symmetry
opposite
quadrilateral
external angle
congruent
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Thank you for your attention