Evaluate the Trigonometric Function Using Its Period as an Aid $\cos \frac { 5 \pi } { 3 }$

Multiple Choice

Evaluate the trigonometric function using its period as an aid.​ $\cos \frac { 5 \pi } { 3 }$ ​

A) $\cos \frac { 5 \pi } { 3 } = \infty$
B) $\cos \frac { 5 \pi } { 3 } = - \frac { 1 } { 2 }$
C) $\cos \frac { 5 \pi } { 3 } = 2$
D) $\cos \frac { 5 \pi } { 3 } = - 2$
E) $\cos \frac { 5 \pi } { 3 } = \frac { 1 } { 2 }$