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Circle Area


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.

Area (A) is the number of square units it takes to cover the surface of a shape. Area is expressed in square units such as cm2, in2, or ft2.
In the circle diagram below, the
shaded part
of the circle is the area.

r = radius
d = diameter
 
diameter = 2 × radius
d = 2 r
Area = π × radius 2
A = π r 2


Example 1: Area answer in terms of π

Find the area in terms of π. Type "pi" in for π so that a correct answer would look like 7pi sq m Area:

The diameter of the circle is 3 yd. To calculate the area of the circle, we will first find the radius of the circle.

d = 2 r
r = = = 1.5 yd
Now we are ready to calculate the area of the circle.
A = π r 2
  = π (1.5 yd)2
  = π (2.25 yd2)
  = 2.25π yd2
The answer is   Area:


Example 2: Area answer with π = 3.14

Find the area. Use 3.14 as an approximation for π. A correct answer would look like 14.5 sq cm.

Using the same problem as Example 1, we know that the area A

A = 2.25π yd2
  = 2.25(3.14) yd2
  = 7.065 yd2
The answer is   Area:

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