Circle Circumference Function: Express in Terms of Radius 'a'

A circle has a radius of a.

Choose the function that expresses its circumference.

The goal of this problem is to find the function that represents the circumference of the circle when the radius is $a$.

The formula for the circumference of a circle is:

• $C = 2\pi r$

We are given that the radius $r$ is $a$.

Using the formula $C = 2\pi r$, substitute $a$ for $r$:

$C = 2\pi a$

Thus, the function that expresses the circumference of the circle is:

$y = 2\pi a$

Among the given choices, $y = 2\pi a$ corresponds to choice number 4.