Question

If diameter of a circle is `5cm.`, find its circumference?

Answer 1

See a solution process below:

Explanation:

The formula for the circumference of a circle is:

`C = 2pir`

Where:

`C` is the circumference of the circle

`r` is the radius of the circle

`2pi` is a constant

Or, because the diameter is twice the radius we can substitute"

`d` for `2r` giving:

`C = dpi`

Substituting gives:

`C = 5cm * pi`

`C = 5pi` centimeters

Answer 2

`5pi` or approximately `15.708` `cm.`

Explanation:

`C=2pir` where `C` is the circumference of the circle, `pi` is the mathematical constant 3.1415..., and `r` is the radius of the circle.

Since `d`, the diameter of the circle, is equal to two times the radius or `2r`, we can see that `C=pid` by substituting `d=2r` into the first equation for the circumference.

Therefore:
`C=pi(5)` or the circumference of the circle is `5pi` or approximately `15.708` `cm.`, rounded to three decimals.