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 then, 2 × 20 = 5 × 8 |
|
=
CB 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 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
