Question

What is the circumference of a circle with diameter 5 inches?

Answer 1

`C = 5pi ~~ 15.708` inches (3 dp)

Explanation:

The circumference of a circle is given by:

`C = 2pir`

Where `r` is the radius, or equivalently

`C = pid`

Where `d=2r` is the diameter.

So, if the diameter is 5 inches then the circumference is:

`C = 5pi ~~ 15.708` inches (3 dp)

Answer 2

Exact circumference = `2pi2.5` in.

Explanation:

The formula for the circumference of a circle is:

`C=2pir`,

where `C` is circumference, `pi` is 3.1415..., and `r` is the radius.

`r=d/2`, where `d` is diameter.

Calculate the diameter.

`r=(5color(white)(.)"in")/2`

`r=2.5color(white)(.)"in"`

Calculate circumference.

`C=2pir`

`C=2xxpixx2.5color(white)(.)"inches"` or `2pi2.5color(white)(.)"inches"` `lArr` This is the exact circumference.

`C=2xxpixx2.5"in"~~15.7color(white)(.)"in"` `lArr` This is an approximate circumference because it is rounded off.