AI generatedGeometry and measuresKey Stage 3

Radius from the area of a circle

Radius from the area of a circle.

  • Use C = 2πr or A = πr², as appropriate.
  • Undo multiplication first; undo the square with a positive square root when needed.

Example 1

A circle has area . Find its radius.

Circle geometry, not to scaleNot to scale
Substitute the given area into A = πr².Take the positive square root because a length is positive.Simplify the root.

Example 2

A circle has area . Find its radius.

Circle geometry, not to scaleNot to scale
Substitute the given area into A = πr².Take the positive square root because a length is positive.Simplify the root.

Your turn

Question 1

A circle has area . Find its radius.

Circle geometry, not to scaleNot to scale
Check answer
Substitute the given area into A = πr².Take the positive square root because a length is positive.Simplify the root.
Question 2

A circle has area . Find its radius.

Circle geometry, not to scaleNot to scale
Check answer
Substitute the given area into A = πr².Take the positive square root because a length is positive.Simplify the root.
Question 3

A circle has area . Find its radius.

Circle geometry, not to scaleNot to scale
Check answer
Substitute the given area into A = πr².Take the positive square root because a length is positive.Simplify the root.
Question 4

A circle has area . Find its radius.

Circle geometry, not to scaleNot to scale
Check answer
Substitute the given area into A = πr².Take the positive square root because a length is positive.Simplify the root.
Question 5

A circle has area . Find its radius.

Circle geometry, not to scaleNot to scale
Check answer
Substitute the given area into A = πr².Take the positive square root because a length is positive.Simplify the root.
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