Circle Theorems

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Circumference and Area

Circumference = Pi x diameter.

e.g. What is the circumference of a circle with a diameter of 4cm? Give your answer to two decimal places.

  • Pi x 4 =12.56cm (2.d.p).

Practice Question: Work out the circumference of the circle when its radius is 6mm. Give your answer to two decimal places.

Area = Pi x radius squared.

e.g. What is the area of a circle with a radius of 3cm? Give your answer to two decimal places.

  • Pi x 3squared = 9.42cm (2.d.p).

Practive Question: Work out the area of a circle with a diameter of 14mm. Give your answer to two decimal places.

Remember: Sometimes exam questions could ask for the circumference of a circle but give you the radius instead of the diameter.

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Angles in a Cyclic Quadrilateral

Angles in a Cyclic Quadrilateral add upto 180 degrees.

(http://www.bbc.co.uk/staticarchive/9ffa5cf1dbd2c28cb54ca81f261dbb31fe07abc2.gif)

E.g. a + c = 180 degrees.

b + d = 180 degrees.

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