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CirclesGeometryMiddle schoolabout 0:59

A circle has radius 0.5. Find its radius, diameter, circumference and area: animated lesson

A narrated, step-by-step circles video lesson with captions. Final answer: r = 1/2, d = 1, C = π ≈ 3.141592654, A = π/4 ≈ 0.7853981634.

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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 0.5. Find its radius, diameter, circumference and area.
2. Step by step
1. $d = 2r = 1$
  Diameter
2. $C = 2\pi r = 2\pi \cdot \frac{1}{2} = \pi \approx 3.141592654$
  Circumference
3. $A = \pi r^2 = \pi \cdot \frac{1}{2}^2 = \frac{\pi}{4} \approx 0.7853981634$
  Area
3. The answer
$r = \frac{1}{2}$
r = 1/2, C = π ≈ 3.141592654, A = π/4 ≈ 0.7853981634
4. Check
- C/d = 3.141592654 = π.
- A = C·r/2 = 0.7853981634.

Transcript

The problem. Here is the problem: A circle has radius 0.5. 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 1 over 2, d equals 1, C equals pi approximately 3.141592654, A equals pi/4 approximately 0.7853981634. 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 0.7853981634.

About circles

Radius, diameter, circumference and area of a circle.

A circle has radius 0.5. Find its radius, diameter…