The function rule
A
=
π
r
2
is a model for the area A of a circle with a radius r. Which of the following represents this equation written in function notation?
A.
A
(
y
)
=
π
r
2
B.
A
(
π
)
=
r
2
C.
A
(
r
)
=
π
r
2
D.
A
(
x
)
=
π
r
2