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CirclesGeometryMiddle schoolabout 0:56

A circle has area 100. Find its radius, diameter, circumference and area: animated lesson

A narrated, step-by-step circles video lesson with captions. Final answer: r = 5.641895835, d = 11.28379167, C = 35.44907702, A = 100.

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Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.4 MB) · Captions (WebVTT)

Steps on screen

1. The problem
Worked example
A circle has area 100. Find its radius, diameter, circumference and area.
2. Step by step
1. $r = \sqrt{\frac{A}{\pi}} = \sqrt{\frac{100}{\pi}} \approx 5.641895835$
  Radius from the area
2. $d = 2r \approx 11.28379167$
  Diameter
3. $C = 2\pi r \approx 35.44907702$
  Circumference
3. The answer
$r = 5.641895835$
r = 5.641895835, C = 35.44907702, A = 100
4. Check
- C/d = 3.141592654 = π.
- A = C·r/2 = 100.

Transcript

The problem. Here is the problem: A circle has area 100. Find its radius, diameter, circumference and area. Find the radius, diameter, circumference and area of a circle from any one of them.

Step by step. Radius from the area. Diameter. Circumference.

The answer. So the answer is r equals 5.641895835, d equals 11.28379167, C equals 35.44907702, A equals 100. Every measurement of a circle follows from its radius. The circumference grows in proportion to the radius and the area in proportion to its square.

Check. C/d equals 3.141592654 equals pi. A equals C times r/2 equals 100.

About circles

Radius, diameter, circumference and area of a circle.

Circles: A circle has area 100. Find its radius, diameter…