Finding the Radius from the Area
(KS3, Year 7)
The LessonThe radius of a circle is found from the area of a circle using the formula:
In this formula, A is the area of the circle. The image below shows what we mean by finding the radius from the area:
How to Find the Radius from the AreaFinding the radius from the area is easy.
QuestionWhat is the radius of the circle, with area 10 cm2, below?
Substitute the area into the formula. In our example, A = 10.
Radius = √ (10⁄π) Radius = √ (10 ÷ π) Radius = √ (10 ÷ 3.14) Radius = √ 3.18 Radius = 1.78 cm
Answer:The radius of the circle is 1.78 cm.
Lesson SlidesThe slider below shows another real example of how to find the radius of a circle from the area. Open the slider in a new tab
Interactive WidgetHere is an interactive widget to help you learn about finding the radius of a circle from its area.
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