Solve the Problem $P$ , Exerted on a Person's Eardrum at a Distance of

Solve the problem.
-In a particular situation, the pressure, $P$ , exerted on a person's eardrum at a distance of 12 feet the source is given by the function: $\mathrm { P } ( \mathrm { t } ) = \frac { \mathrm { a } } { 12 } \cos ( 2 \mathrm { n } \pi - \mathrm { ct } )$ , where $\mathrm { n }$ is a positive integer. Use difference identity for cosine to simplify $\mathrm { P }$ in this situation.

A) $\mathrm { P } ( \mathrm { t } ) = \frac { \mathrm { a } } { 12 } \cos ( \mathrm { ct } ) - \frac { \mathrm { a } } { 12 } \sin ( \mathrm { ct } )$
B) $P ( t ) = \frac { a } { 12 } \cos ( c t )$
C) $P ( t ) = \frac { 12 } { 13 } \cos ( c t + 12 )$
D) $\mathrm { P } ( \mathrm { t } ) = \cos ( \mathrm { ct } )$