10/4

10/4

Bell Activity: How many triangles are there in this diagram?

Two Dimensional Shapes

Learning objectives

• Be able to find the area and circumference of a circle

The perimeter of this shape has a special name. What is it?

My perimeter is calledThe Circumference

These things are very important in calculating the circumference of a circle.

Remember a round pi (spelled wrong)

Pi

Pi is a large number that goes on forever

But we use 3.14 to be approximately equalto pi.

r

d

r = radiusd = diameter

To calculate the circumference of a circleYou do3.14 x dOr2 x 3.14 x r Look at Mr Lock’s example on the board.

Use your calculator to calculate the circumference of these shapes

To calculate the circumference of a circleYou do3.14 x dOr2 x 3.14 x r

11cm

3cm

1.56cm

This circle has circumference 298cm².

What do you think it’s diameter is?

It’s radius?

Area of a circle

• For this, you have to know the radius

• The area is given by

• A = π X r²

• (remember to square the radius before multiplying)

Try these

5cm

2.5cm

13cm

Find the area of this shape…

24.6cm

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)

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)