Question

How do you find the perimeter or circumference, and the area of a circle with radius 4.2 in?

Answer 1

See a solution process below:

Explanation:

The formula for the perimeter or circumference of a circle is:

`C= 2pir`

The formula for the area of a circle is:

`A_c = pir^2`

In both formulas `r` represents the radius of the circle.

Substituting `4.2" in"` for `r` in both formulas gives:

Circumference:

`C= 2pir` becomes:

`C= 2pi * 4.2" in"`

`C= 8.4pi" in"`

If you need a number we can substitute `3.14` for `pi` giving:

`C = 8.4 * 3.14" in" = 26.376" in"`

Area:

`A_c = pir^2` becomes:

`A_c = pi * (4.2" in")^2`

`A_c = 17.64pi" in"^2`

Again, if you need a number we can substitute `3.14` for `pi` giving:

`A_c = 17.64 * 3.14" in"^2 = 55.3896" in"^2`