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The Perimeter Of A Shape. 10m Regular Octagon 6cm 4cm 5cm 3cm 4cm.

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Presentation on theme: "The Perimeter Of A Shape. 10m Regular Octagon 6cm 4cm 5cm 3cm 4cm."— Presentation transcript:

1 The Perimeter Of A Shape. 10m Regular Octagon 6cm 4cm 5cm 3cm 4cm

2 The Idea Of Perimeter. Perimeter is the distance around the outside of a shape. What is the perimeter of the shapes below ? (1) 6cm 4cm (2) 5.6m 8.9m P =6 +4 +6 +4 P =20cm P =2 x( 5.6 + 8.9) P = 29m

3 (3) 5cm 3cm 4cm P =3 +4 +5 P =12cm (4) 10m Regular Octagon P =8 x10 P =80 m

4 What Goes In The Box ? Calculate the perimeter of the shapes below: (1) 9 cm 4cm (2) 9.7cm 11.4cm (3) 7.8 m 10.3m 8.1m 7.9m (4) 12cm P = 26cmP=32.5cm P = 34.1mP=72cm

5 The Perimeter Of A Circle. Look at the circle below: What do we call the distance around the circle? Circumference. What do we call the distance across the circle ? Diameter Key Question. How many times bigger is the diameter of the circle compared to the diameter ? The circumference is a bit more than three times the diameter.

6 Estimating The Circumference. If we know that the circumference of a circle is roughly three times the diameter, then estimate the circumference of the circles below: (1) 6cm Circumference = 3 x diameter C = 3 x6cm C = 18 cm (2) 9m Circumference = 3 x diameter C = 3 x9m C = 27m

7 Key Fact. They found that the circumference was 3.14 times bigger than the diameter. They called 3.14 Pi after a letter in the Greek alphabet. The letter pi is written as : The Number Called Pi. After a great deal of measuring and calculating, Greek mathematicians came up with a better estimate of how many times bigger the circumference was compared to the diameter. The Circumference Of A Circle. Circumference = Pi x Diameter

8 Calculating The Circumference. (1) 10m Calculate the circumference of the circles below: C = x D = 3.14 D = 10m C = 3.14 x 10 C = 31.4m (2) 2.8cm C = x D = 3.14 D = 2.8cm C = 3.14 x 2.8 C = 8.8cm

9 What Goes In The Box 2 ? Calculate the circumference of the circles shown below: (1) 4cm (2) 26cm (3) 2.3m 12.6cm 81.64m 14.4m

10 Perimeter Of More Complex Shapes. Calculate the perimeter of the shapes below: (1) 12m P = D + ( D) 2 P = 12 + (3.14 x12) 2 P = 12 + 18.84 P = 30.8 cm

11 (2) 10 m 8 m P =10 +16 + (3.14 x10 2) P =26 +15.7 P = 41.7m

12 (3) 10cm P =10 + (3.14 x 20) x 0.75 P =20 +47.1 P =67.1 cm


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