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

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.