We need to know the names of different parts of a circle:

The two most important measurements we need to be able to calculate about a circle are the size of its area and the length of its circumference. To calculate both of these we use the special number π (pi).

Using what we know already (including the fact that there are 360º in a circle, we can find the area and the arc length of a sector of a circle, provided we know the radius – let’s look with our teacher at how we calculate this.

Let’s do some examples on the board where we calculate areas and perimeters (circumferences?) of circles and sectors. (we will probably need a calculator for these as π is not an integer. To approximate for it we can use 3.14).

Exercise

Let’s complete exercise 17A on pages 282 to 283 of the textbook:

The answers are below: