The "pizza" slice is called a Sector. And the slice made by a chord is called a Segment. Ellipse A circle is a "special case" of an ellipse. Activity: Approximate Value For Pi.
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. The diameter is the length, or distance, across the circle at its widest point, passing through the center.
Another related measurement, the radius, is a line that goes from the center to the circle's edge. The diameter is equal to 2 times the radius. A line that goes across the circle, but not at its widest point, is called a chord. The circumference is the perimeter, or distance around the circle.
Imagine wrapping a string all the way around a circle. Now imagine removing the string and pulling it out into a straight line. If you were to measure this string, that length is the circumference of your circle. The quantity pi is a mathematical constant defined as the ratio of a circle's circumference to its diameter. In other words, the distance surrounding a circle is known as the circumference of the circle.
The diameter is the distance across a circle through the centre, and it touches the two points of the circle perimeter. The circumference formula is pi times diameter or 2 times pi times radius, so if the circumference is given, the radius would be the circumference divided by 2pi.
The result is the circle's diameter. Divide the diameter by 2. There you go, you found the circle's radius. In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel.
It's not really tricky. Or to put it another way, the circumference is approximately 3 times bigger than the diameter.
In this case, the diameter would be 3.
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