Circles
The circumference is the distance around a circle and the area is the space inside. Both use pi, which is about 3.14.
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Analogy
Circumference is the length of a bike tyre. Area is the size of a pizza.
Example
Circumference = 2 x pi x 5 = 10 x pi = 31.4Area = pi x 5^2 = 25 x pi = 78.5
In practice
Knowing the circumference tells you how far a wheel travels in one turn.
Practice
Flashcards
- What is the area of a circle with radius 5?About 78.5, from pi x 5^2.
Questions people ask
What is the difference between radius and diameter?
The radius goes from the centre to the edge. The diameter goes right across through the centre, so it is twice the radius. If a circle has a diameter of 10, then its radius is 5. Always check which one a question gives you.
What is pi?
Pi is the number you get when you divide a circle's circumference by its diameter, for every circle. It is roughly 3.14, but its decimals never end or repeat. Calculators have a pi button for more accuracy than 3.14. It is used in every circle formula.