Verify That the Equation Is an Identity $\mathrm { V } = 164 \cos \left( 2 \pi \mathrm { ft } - \frac { \pi } { 6 } \right)$

Verify that the equation is an identity.
-The output voltage of a generator is given by $\mathrm { V } = 164 \cos \left( 2 \pi \mathrm { ft } - \frac { \pi } { 6 } \right)$ . Express the voltage as the sum of a sine and a cosine function.

A) $V = 82 \sqrt { 3 } \cos 2 \pi f t - 82 \sin 2 \pi f t$
B) $\mathrm { V } = 82 \cos 2 \pi \mathrm { ft } + 82 \sin 2 \pi \mathrm { ft }$
C) $\mathrm { V } = 82 \sqrt { 3 } \sin 2 \pi \mathrm { ft } + 82 \cos 2 \pi \mathrm { ft }$
D) $V = 82 \sqrt { 3 } \cos 2 \pi f t + 82 \sin 2 \pi f t$