Circle
A circle is easy to make:
Draw a curve that is "radius" away
from a central point.
And so:
All points are the same distance from the center.
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You Can Draw It Yourself
Put a pin in a board, put a loop of string around it, and insert a pencil into the loop. Keep the string stretched and draw the circle!
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Drag a point!
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Play With It
Try dragging the point to see how the radius and cirfcumference change.
Radius, Diameter and Circumference
The Radius is the distance from the center outwards.
The Diameter goes straight across the circle, through the center.
The Circumference is the distance once around the circle.
And here is the really cool thing:
So when the diameter is 1, the circumference is 3.141592654...
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We can say:
Circumference = π × Diameter
Also note that the Diameter is twice the Radius:
Diameter = 2 × Radius
And so this is also true:
Circumference = 2 × π × Radius
Remembering
The length of the words may help you remember:
- Radius is the shortest word
- Diameter is longer (and is 2 × Radius)
- Circumference is the longest (and is π × Diameter)
Definition
The circle is a plane shape (two dimensional):
And the definition of a circle is:
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The set of all points on a plane that are a fixed distance from a center.
A circle has about 80% of the area of a similar-width square.
The actual value is (π/4) = 0.785398... = 78.5398...%
The actual value is (π/4) = 0.785398... = 78.5398...%