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CirclesGeometryMiddle schoolabout 1:01

A circle has radius 12. Find its radius, diameter, circumference and area: animated lesson

A narrated, step-by-step circles video lesson with captions. Final answer: r = 12, d = 24, C = 24π ≈ 75.39822369, A = 144π ≈ 452.3893421.

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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 radius 12. Find its radius, diameter, circumference and area.
2. Step by step
1. $d = 2r = 24$
  Diameter
2. $C = 2\pi r = 2\pi \cdot 12 = 24\pi \approx 75.39822369$
  Circumference
3. $A = \pi r^2 = \pi \cdot 12^2 = 144\pi \approx 452.3893421$
  Area
3. The answer
$r = 12$
r = 12, C = 24π ≈ 75.39822369, A = 144π ≈ 452.3893421
4. Check
- C/d = 3.141592654 = π.
- A = C·r/2 = 452.3893421.

Transcript

The problem. Here is the problem: A circle has radius 12. 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. Diameter. Circumference. Area.

The answer. So the answer is r equals 12, d equals 24, C equals 24pi approximately 75.39822369, A equals 144pi approximately 452.3893421. 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 452.3893421.

About circles

Radius, diameter, circumference and area of a circle.

A circle has radius 12. Find its radius, diameter…