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Parts of a circle

Parts of a circle

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Tutor: Holly

Summary

Parts of a circle

​​In a nutshell

A circle is a 2D plane shape where all the points are an equal distance from the centre.


Parts of a circle

​Circles can be described by diameter, radius and circumference.


​​​​Definitions

  • ​Diameter - The distance, through the centre, across the circle (twice the radius).
  • Radius - The distance from the edge to the centre of the circle (half the diameter).
  • Circumference - The distance around the edge of the circle.


Insert image showing diameter, radius and circumference of a circle.


The diameter of a circle is double the length of the radius.  It can be written as:

​d=2rd = 2rd=2r

​r=12dr=\frac{1}{2}dr=21​d​​


Where ddd is the diameter of the circle, and rrr is the radius of the circle.​


Example

The radius of a circle is 4.8cm4.8cm4.8cm​. What is the diameter of the circle?


First, write out the known quantity:

r=4.8 cmr = 4.8 \space cmr=4.8 cm


Then, write the formula for the diameter of a circle:

d=2rd = 2rd=2r​​


Next, substitute the known quantity into the formula:

d=2×4.8d = 2 \times 4.8d=2×4.8


Don't forget to include the units:​

9.6 cm9.6 \space cm9.6 cm


The diameter of the circle is 9.6cm‾\underline{9.6cm}9.6cm​​

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2D shapes: Types and properties

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2D shapes: Types and properties

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Parts of a circle

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Parts of a circle

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FAQs - Frequently Asked Questions

What is the circumference of a circle?

The circumference of a circle is the distance around the edge of the circle.

What is the radius of a circle?

The radius of a circle is the distance from the edge to the centre of the circle (half the diameter).

What is the diameter of a circle?

The diameter of a circle is the distance, through the centre, across the circle (twice the radius).

What is a circle?

A circle is a 2D plane shape where all the points are an equal distance from the centre.

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