Model the Curve with a Cosine Function $P = \frac { 1 } { 3 }$

Multiple Choice

Model the curve with a cosine function.
Note that the period of the curve is $P = \frac { 1 } { 3 }$ and its range is $[ - 1,1 ]$ .

A) $f ( x ) = \cos ( 6 x )$
B) $f ( x ) = \cos ( 6 \pi x )$
C) $f ( x ) = \cos \left( \frac { x } { 6 } \right)$
D) $f ( x ) = \cos \left( \frac { \pi x } { 6 } \right)$
E) $f ( x ) = 6 \cos ( \pi x )$