Find the Formula for the Function $A = \pi r ^ { 2 }$

Multiple Choice

Find the formula for the function.
-Express the area of a circle as a function of its radius r.

A) A = 2 r
B) A = r
C) $A = \pi r ^ { 2 }$
D) $\mathrm { A } = \pi \mathrm { r } ^ { 3 }$