Geometry Perimeter of 2D Shapes Starter: It’s a Match Task: Match up the name to its shape. There may be more than one answer as well as some red herrings! Triangle Square Rectangle Parallelogram Trapezium Extension: Choose a shape and describe its properties using the keywords vertices, faces and edges, lines of symmetry, parallel, angles. Starter: It’s a Match - Answers Rectangle Triangle Trapezium Square Parallelogram What Is Perimeter? Pause for Thought What is ‘perimeter’? Can you think of a definition? To calculate the perimeter, we add up the lengths of all of its sides. The perimeter of a shape is the total distance around its edge. Pause for Thought How do we calculate perimeter? When Will I Need Perimeter? Pause for Thought Can you think of any real-life examples of when you might need to calculate a perimeter? Gardening Decorating houses Building projects Farming Wrapping presents Fencing off an area Calculating Perimeter Calculate the perimeter of this square. 5cm 5 + 5 + 5 + 5 = 20cm or 5 × 4 = 20cm Too easy? Try this! Calculate the perimeter of a square where one side is equal to 4 + 2 × 2cm. 4+2×2=8 8+8+8+8 or 8 × 4 = 32cm Calculating Perimeter Calculate the perimeter of this rectangle. 10cm 4cm 10 + 4 + 10 + 4 = 28cm or (10 + 4) × 2 = 28cm Too easy? Try this! Calculate the perimeter of a rectangle where the width is 5cm and the length is 0.2m. Give your answer in centimetres. 0.2m = 20cm (20 + 5) × 2 = 50cm Calculating Perimeter Calculate the perimeter of this triangle. 8cm 4cm 10 + 8 + 4 = 22cm 10cm Too easy? Try this! Calculate the perimeter of an equilateral triangle, which has a side length of 6cm. 6 × 3 = 18cm Calculating Perimeter Calculate the perimeter of this parallelogram. 11cm 7cm 11 + 7 + 11 + 7 = 36cm or (11 + 7) × 2 = 36cm Too easy? Try this! Calculate the perimeter of a parallelogram where the width is 0.15m and the length is 20cm. Give your answer in centimetres. 0.15m = 15cm (20 +15) × 2 = 70cm Calculating Perimeter Calculate the perimeter of this trapezium. 6cm 7cm 7cm 12 + 7 + 6 + 7 = 32cm 12cm Too easy? Try this! Calculate the perimeter of a trapezium which has the measurements of 10cm, 8cm, 0.12m and 70mm. Give your answer in centimetres. 0.12m = 12cm 70mm = 7cm 10 + 8 + 12 + 7 = 37cm Calculating Perimeter What is the total perimeter for the following shape? 3cm 4cm Pause for Thought What information is missing? 9cm 10cm 6cm 12cm 12 + 10 + 3 + 4 + 9 + 6 = 44cm
