## Answers in terms of π

A more accurate answer, when calculating circle-based objects, can be obtained by not using a value of π, but to leave it as a constant.

Questions may ask for the answer to be given in terms of π. In this instance, do not use a value for π, show the answer instead as a multiple of π.

## Example 1

A circle has a radius of 8 cm. What is the area of the circle?

Give your answer in terms of π.

 Area of a circle: A  = pir^2 Substitute: A  = pi xx 8^2 In terms of pi: A  = 64pi

Answer: 64π cm2

## Example 2

A surface radar is sweeping an arc of 60º; with a range of 12km. What is the surface area being swept by the radar?

Give your answer in terms of π.

Area of a circle is given by A = πr2.

Area of whole circle = π x 122 = 144π

But the radar is sweeping 60/360º of a whole circle,

 Area being swept: A = 144π x frac(60)(360) = 144π ÷ 6 In terms of pi: = 24pi

Answer: 24π km2