Download Lesson 8. Triangles and Quadrilaterals

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
Trapezium
Four equal sides
One pair of opposite sides parallel
All angles 90º
Four lines of symmetry
Rotational symmetry of order 4
No lines of symmetry
No rotational symmetry
You need W/S 8.2B
Example
Using a 3 by 3 pinboard draw as many
different triangles as you can find.
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.
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
The marked angle is angle
ADC or angle CDA.
Sometimes written as <ADC
D
C
ˆ
or ADC
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?
D
C
Obtuse
C
AB has been extended to point D.
Angle CBD (marked) is an external
angle of the triangle.
A
B
D
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