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