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**Triangles and Quadrilaterals**

Level 4/5 Booster Lesson 8B Triangles and Quadrilaterals

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**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

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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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**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

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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.

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**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?

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**Here are the quadrilaterals you can find.**

Other shapes you can produce are:

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**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

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**Thank you for your attention**

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