## Presentation on theme: "Triangles and Quadrilaterals"— Presentation transcript:

Level 4/5 Booster Lesson 8B Triangles and Quadrilaterals

rotational symmetry parallel opposite quadrilateral external angle
Objectives: To identify and use the properties of triangles and quadrilaterals. Vocabulary: parallel rotational symmetry opposite quadrilateral external angle congruent

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 No lines of symmetry Four lines of symmetry No rotational symmetry Rotational symmetry of order 4

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.

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?

ˆ Conventional labelling: A B
The marked angle is angle ADC or angle CDA. Sometimes written as <ADC or ADC D ˆ C How would you describe the angle indicated in the same way? A B C D Estimate the size of angle BAD. º What type of angle is angle ADC? Obtuse

A B C AB has been extended to point D. Angle CBD (marked) is an external angle of the triangle. 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
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:

rotational symmetry parallel opposite quadrilateral external angle
Objectives: To identify and use the properties of triangles and quadrilaterals. Vocabulary: parallel rotational symmetry opposite quadrilateral external angle congruent