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# Circumference of a circle utilizing the circumference system

The circumference of a circle will be discovered utilizing both C = π × d or C = 2 × π × r. The lesson about the quantity π reveals tips on how to derive the system. If both the radius of a circle (r) or the diameter of the circle (d) is understood, you will discover the circumference by merely substituting the recognized worth for r or d within the system. Use 3.14 for π.

## A couple of examples exhibiting tips on how to discover the circumference of a circle

Examples #1

Calculate the circumference of a circle if r = 2 inches

C = 2 × π × r = 2 × 3.14 × 2 = 12.56 inches

Examples #2

Calculate the circumference of a circle if r = 4 inches

C = 2 × π × r = 2 × 3.14 × 4 = 25.12 inches

Examples #3

If D = 10 cm, discover the circumference.

You’ve two selections. You possibly can first discover r after which substitute its worth for r within the system.

r is half the diameter, so r = 10 divided by 2

r = 5 cm

C = 2 × π × r = 2 × 3.14 × 5 = 31.4 cm

In any other case, you may simply use the system C = π × D

C = 3.14 × 10 = 31.4 cm

## A difficult train in regards to the circumference of a circle

Examples #4

The circumference of circle A is 4 instances the circumference of circle B

The diameter of circle B is 7. What’s the diameter of circle A?

Let CA be the circumference of circle A

Let CB be the circumference of circle B

Let DA be the diameter of circle A

Let DB be the diameter of circle B

Because the ratio of circumference to diameter is identical for all circles, you should use the next proportion to resolve this downside.

Issues that we all know:

CA = 4 × CB

DB = 7

Substitute these within the proportion

 =    8 / 20   then, 2 × 20 = 5 × 8

 =    CB / 7   then, 4 × CB × 7 = DA × CB

28 × CB = DA × CB

DA = 28 since 28 × CB = 28 × CB it doesn’t matter what CB is

Issues that we all know:

CA = 4 × CB

DB = 7

Substitute these within the proportion

 =    8 / 20   then, 2 × 20 = 5 × 8

Then, 4 × CB × 7 = DA × CB

28 × CB = DA × CB

DA = 28 since 28 × CB = 28 × CB it doesn’t matter what CB is

## Circumference of a circle quiz. See how effectively you may calculate the circumference or perimeter of a circle

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