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Home > Maths I > Measure and Shape > Area and circumference of a circle

Maths I

Area and circumference of a circle

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In your General Exam you may have to work out - the circumference of a circle; the area of a circle; the perimeter of a semicircle; the area of a semicircle and the area of a combined shape including a semicircle.

# The area and the circumference of a circle

Make sure that you remember that a circumference is a length and so is measured , , etc. Remember as well that area is measured in square units, , etc. All of these calculations will involve the use of Pi () which you can take as being equal to . A formula list is given in the exam so you don't need to remember all the formulae but you do have to remember how to use them.

## The circumference of a circle

For any circle with a diameter, , the circumference, , is found by using the formula

For this circle:

=

=

Remember that, for any circle, the diameter is twice the radius, or .

If we are told the radius instead of the diameter we use the formula -

For this circle:

=

=

## The area of a circle

For any circle with radius, , the area, , is found using the formula

For this circle:

=

=

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