#### Revision Notes

##### Why are circles different to other 2D shapes?

Circles just have their own language!

The circumference of a circle is its perimeter.

is the number (3.14159 …) that links a circle’s diameter to its circumference.

Diameter (d) is twice the radius (r).

You may be asked to give an area answer to a certain number of decimal places or significant figures. Alternatively you may be asked to give the exact value – or “give your answer in terms of ” – so this topic could crop up on the non-calculator paper!

##### Working with circles

You must know the formulas for the Area and Circumference of a circle.

There are two versions for the Circumference and it is important not to get the radius and diameter confused. Remember that d = 2r. But you may prefer to remember the formulas by having different letters involved.

Other than that, working with circle formulas is just like working with any other formula:

1. WRITE DOWN – what you know
– what you want to know
2. Pick correct FORMULA
3. SUBSTITUTE and SOLVE

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### Author: Simon

After 24 years teaching A Level Further Maths, Maths whizz Simon focused his attention on tutoring. He’s helped thousands of young people make sense of Maths and now he’s helping you too – aren’t you lucky! He’s even worked as an Edexcel examiner, so knows exactly what they’re looking for.