Summary Circumference-and-Area.docx

Topic/Skill Definition/Tips
Topic: Circumference and Area Example
1. Circle A circle is the locus of all points equidistant
from a central point.


2. Parts of a Radius – the distance from the centre of a
Circle circle to the edge
Diameter – the total distance across the
width of a circle through the centre.
Circumference – the total distance around
the outside of a circle
Chord – a straight line whose end points
lie on a circle
Tangent – a straight line which touches a
circle at exactly one point
Arc – a part of the circumference of a
circle
Sector – the region of a circle enclosed by
two radii and their intercepted arc
Segment – the region bounded by a chord
and the arc created by the chord
3. Area of a A=π r 2 which means ‘pi x radius squared’. If the radius was 5cm, then:
Circle 2
A=π × 5 =78.5 cm
2

4. C=πd which means ‘pi x diameter’ If the radius was 5cm, then:
Circumference C=π × 10=31.4 cm
of a Circle
5. π (‘pi’) Pi is the circumference of a circle divided
by the diameter.

π ≈3.14


6. Arc Length The arc length is part of the circumference. 115
Arc Length = × π ×8=8.03 cm
of a Sector 360
Take the angle given as a fraction over
360° and multiply by the circumference.




7. Area of a The area of a sector is part of the total area. 115 2 2
Area = × π × 4 =16.1 cm
Sector 360
Take the angle given as a fraction over
360° and multiply by the area.




Mr A. Coleman Glyn School