Area & Circumference of Circles (Cambridge O Level Maths)

Why are circles different to other 2D shapes?

• Circles are a shape that is made up of all the points on a 2D plane that are equidistant from a single point
  • Equidistant means the same distance
• The circumference of a circle is its perimeter
• π (pi) is the number (3.14159 …) that links a circle’s diameter to its circumference
• 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 π” – so this topic could crop up on the non-calculator paper!

How do I work with circles?

• You must know the formulae 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 formulae by having different letters involved

• Working with circle formulae is just like working with any other formula:
  • WRITE DOWN – what you know (what you want to know)
  • Pick correct FORMULA
  • SUBSTITUTE and SOLVE