The document discusses calculating the circumference and area of circles using pi and radius or diameter. It provides examples of calculating circumference given the diameter or radius. It also discusses calculating the area of a circle using the radius and the formula area = π x radius2. Finally, it asks the reader to find the area of a circle with a 12cm diameter and 4cm radius without looking back at prior examples.

1. 10/4 Bell Activity: How many triangles are there in this diagram?

2. Two Dimensional Shapes Learning objectives Be able to find the area and circumference of a circle

3. The perimeter of this shape has a special name. What is it? My perimeter is called The Circumference

4. These things are very important in calculating the circumference of a circle. Remember a round pi (spelled wrong)

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. 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. This circle has circumference 298cm ². What do you think it’s diameter is? It’s radius?

8. Area of a circle For this, you have to know the radius The area is given by A = π X r ² (remember to square the radius before multiplying)

9. Try these 5cm 2.5cm 13cm

10. Find the area of this shape… 24.6cm

11. How the heck would you do this then? 5 mins. Like an exam I want an answer What Would You Do? 12cm 4cm Find the area….. (435 marks)

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)