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Here are some tips for Circle Measurements, which aligns with California state standards:

Circle Measurements


For this topic, you will need to know how to find the length of a line segment on a graph.
To review the Line Segments topic, see here.

A circle is a shape where all points are the same distance from the center of the circle. The radius (r) of a circle is the distance from the center of the circle to any point on the circle. The diameter (d) of a circle is the distance across the circle through the center.

r = radius
d = diameter		  
diameter = 2 × radius
d = 2 r


Example 1:

Find the radius and diameter of the circle.
Radius: Diameter:
To find the radius, count the number of units from the center of the circle to any point on the circle.
For example, the center of the circle is located at (3,2) and the top point of the circle is located at (3,6). The distance between the two points is the radius of the circle.
Therefore, the radius is 6 - 2 = 4.

To find the diameter, you can either

  1. Double the radius: 4 × 2 = 8
    OR
  2. Count the number of units across the circle through the center:
    The distance between (3,6) and (3,-2) is 8
The answer is Radius: Diameter:

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