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CirclesGeometryMiddle schoolabout 1:01

A circle has diameter 7. Find its radius, diameter, circumference and area: animated lesson

A narrated, step-by-step circles video lesson with captions. Final answer: r = 7/2, d = 7, C = 7π ≈ 21.99114858, A = 49π/4 ≈ 38.48451001.

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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 diameter 7. Find its radius, diameter, circumference and area.
2. Step by step
1. $r = \frac{d}{2} = \frac{7}{2}$
  Radius from the diameter
2. $C = 2\pi r = 2\pi \cdot \frac{7}{2} = 7\pi \approx 21.99114858$
  Circumference
3. $A = \pi r^2 = \pi \cdot \frac{7}{2}^2 = \frac{49\pi}{4} \approx 38.48451001$
  Area
3. The answer
$r = \frac{7}{2}$
r = 7/2, C = 7π ≈ 21.99114858, A = 49π/4 ≈ 38.48451001
4. Check
- C/d = 3.141592654 = π.
- A = C·r/2 = 38.48451001.

Transcript

The problem. Here is the problem: A circle has diameter 7. 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 diameter. Circumference. Area.

The answer. So the answer is r equals 7 over 2, d equals 7, C equals 7pi approximately 21.99114858, A equals 49pi/4 approximately 38.48451001. 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 38.48451001.

About circles

Radius, diameter, circumference and area of a circle.

A circle has diameter 7. Find its radius, diameter…