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# 2 Dimensional Shapes 2

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### 2 Dimensional Shapes 2

1. 1. 10/4 Bell Activity: How many triangles are there in this diagram?
2. 2. Two Dimensional Shapes <ul><li>Learning objectives </li></ul><ul><li>Be able to find the area and circumference of a circle </li></ul>
3. 3. The perimeter of this shape has a special name. What is it? My perimeter is called The Circumference
4. 4. These things are very important in calculating the circumference of a circle. Remember a round pi (spelled wrong)
5. 5. Pi Pi is a large number that goes on forever But we use 3.14 to be approximately equal to pi. r d r = radius d = diameter To calculate the circumference of a circle You do 3.14 x d Or 2 x 3.14 x r Look at Mr Lock’s example on the board.
6. 6. Use your calculator to calculate the circumference of these shapes To calculate the circumference of a circle You do 3.14 x d Or 2 x 3.14 x r 11cm 3cm 1.56cm
7. 7. This circle has circumference 298cm ². What do you think it’s diameter is? It’s radius?
8. 8. Area of a circle <ul><li>For this, you have to know the radius </li></ul><ul><li>The area is given by </li></ul><ul><li>A = π X r ² </li></ul><ul><li>(remember to square the radius before multiplying) </li></ul>
9. 9. Try these 5cm 2.5cm 13cm
10. 10. Find the area of this shape… 24.6cm
11. 11. How the heck would you do this then? <ul><li>5 mins. Like an exam </li></ul><ul><li>I want an answer </li></ul><ul><li>What </li></ul><ul><li>Would </li></ul><ul><li>You </li></ul><ul><li>Do? </li></ul>12cm 4cm Find the area….. (435 marks)
12. 12. Without looking back, write down how you construct a triangle using ruler and compasses Now write down 6 quadrilaterals (and how to find their area)