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Objectives:
•To identify and use the properties of triangles and quadrilaterals.
Vocabulary:
Name the quadrilaterals and state their identifying properties:
W/S 8.1B
Parallelogram
Opposite sides equal
Opposite sides parallel
No lines of symmetry
Rotational symmetry order 2
Rectangle
Opposite sides equal (and parallel)
All angles 90º
Two lines of symmetry
Rotational symmetry of order 2
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
Square
Four equal sides
All angles 90º
Four lines of symmetry
Rotational symmetry of order 4
Trapezium
One pair of opposite sides parallel
No lines of symmetry
No rotational symmetry
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.
You need W/S 8.2B
Here are the 8 different triangles that are possible.
Which of these triangles have an obtuse angle?
Which of these triangles are isosceles?
Which of these triangles contain a right angle?
Conventional labelling:
A B
CD
The marked angle is angle ADC or angle CDA.
Sometimes written as <ADC
or ADCˆ
How would you describe the angle indicated in the same way?
AB
C
D
Estimate the size of angle BAD.
What type of angle is angle ADC?
50 - 60º
Obtuse
D
AB has been extended to point D.
Angle CBD (marked) is an external angle of the triangle.
A B
C
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.
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?
Here are the quadrilaterals you can find.
Other shapes you can produce are:
Objectives:
•To identify and use the properties of triangles and quadrilaterals.
Vocabulary:
Thank you for your attention