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Circles and Circumference

This topic covers the concepts of parts of circles and their circumference.

Topic: Parts of a Circle

  • A circle is the set of all points in a plane that are at the same distance from a given point, called the center. A circle is named by its center

  • A diameter is a line segment that passes through the center of the circle and has both the end points on the circle

  • A radius is a line segment with one endpoint at the center of the circle and the other endpoint on the circle

  • The distance around a circle is called the circumference. The ratio of the circumference to the diameter, C/d, is the same for any circle and is called ∏, read as "pi"

  • The value of p is approximated to either 3.14 or 22/7

Topic: Circumference of a Circle

  • The length of the diameter is twice the length of the radius. Or, d = 2 x r

  • The circumference of any circle is equal to p times the diameter.
    The formula for the circumference of a circle is C = pd

  • Replacing the value of d = 2 x r in the formula for circumference, we get:
    C = 2pr

Topic: Word Problems

  • Circumference of a circle = pd = 2pr

  • The ratio of the circumference to the diameter, C/d, is the same for any circle and is called p, read as "pi"

  • The ratio of the radius of a circle to the diameter of a circle is always 1/2

  • Distance covered in one full turn of a circle = Circumference of the circle

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