A simple way to find the radius of a circle if you know the circumference of the circle


The example below illustrates clearly how to find the radius of a circle when the circumference is known. Suppose the circumference of a circle is 50.24 inches, calculate r.

Solution

find the radius of a circle given circumference

Here are the steps to follow:

Step 1:

Write down the circumference formula.

Step 2:

Replace the circumference with 50.24 inches.

Step 3

Since you are looking for r, you need to get rid of 2 × pi. You do this by dividing both sides by 2 × pi.

Step 4

Notice that now the number next to r is just 1 and 1 times r is r. To get the answer, you just have to divide 50.24  inches by 6.28. When the circumference of a circle is 50.24 inches, the radius is 8.

The example above illustrates a simple but long way to solve this problem. You can find the radius of a circle very quickly by dividing the value of any circumference by 6.28.

Example 2:

Find r when the circumference is 31.4

r = 31.4 / 6.28 = 5.

Yes, it is that simple yet you still need to know how to do it by following the steps above.

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