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Circles for SQA National 5 Maths

Circles

This page covers the following topics:

1. Radius and diameter of a circle
2. Circumference of a circle
3. Area of a circle

The radius of a circle is the distance between the centre of a circle and the edge. The diameter of a circle is the distance between two edges of a circle passing through the centre. The diameter is double the size of the radius.

Radius and diameter of a circle

The circumference of a circle can be calculated using the following formula: C = 2ฯ€r, where r is the radius of a circle.

Circumference of a circle

The area of a circle is given by the formula: A = ฯ€rยฒ, where r is the radius of the circle.

Area of a circle

1

Calculate the area of a circle with radius 5 cm.

A = ฯ€(5 cm)ยฒ = 25ฯ€ cmยฒ = 78.5 cmยฒ (to 3 significant figures).

Calculate the area of a circle with radius 5 cm.

2

Given that r = 8 cm, calculate the circumference of the given circle.

C = 2ฯ€(8 cm) = 16ฯ€ cm = 50.3 cm (to 3 significant figures).

Given that r = 8 cm, calculate the circumference of the given circle.

3

Sketch a diagram of a circle, labelling for its radius and diameter.

image

Sketch a diagram of a circle, labelling for its radius and diameter.

4

Given that the radius of a circle is 4 cm, calculate the length of its diameter.

Diameter = 2(4) = 8 cm.

Given that the radius of a circle is 4 cm, calculate the length of its diameter.

5

Use the given diagram to calculate the diameter of the circle.

The radius of the circle is 1.2 m.
So, the diameter = 2(1.2) = 2.4 m.

Use the given diagram to calculate the diameter of the circle.

End of page

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