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CirclesGeometryMiddle schoolabout 1:04

A circle has circumference 31.4. Find its radius, diameter, circumference and area: animated lesson

A narrated, step-by-step circles video lesson with captions. Final answer: r = 4.997465213, d = 9.994930426, C = 31.4, A = 78.46020385.

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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 circumference 31.4. Find its radius, diameter, circumference and area.
2. Step by step
1. $r = \frac{C}{2\pi} = \frac{\frac{157}{5}}{2\pi} \approx 4.997465213$
  Radius from the circumference
2. $d = 2r \approx 9.994930426$
  Diameter
3. $A = \pi r^2 \approx 78.46020385$
  Area
3. The answer
$r = 4.997465213$
r = 4.997465213, C = 31.4, A = 78.46020385
4. Check
- C/d = 3.141592654 = π.
- A = C·r/2 = 78.46020385.

Transcript

The problem. Here is the problem: A circle has circumference 31.4. 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 circumference. Diameter. Area.

The answer. So the answer is r equals 4.997465213, d equals 9.994930426, C equals 31.4, A equals 78.46020385. 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 78.46020385.

About circles

Radius, diameter, circumference and area of a circle.

Circles: A circle has circumference 31.4. Find its radius…