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Download Lesson 8. Triangles and Quadrilaterals
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Transcript
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