Use the Value of the Trigonometric Function to Find $\cos ( t + \pi )$

Multiple Choice

Use the value of the trigonometric function to find $\cos ( t + \pi )$ .​ $\cos t = \frac { 7 } { 8 }$ ​

A) $\cos ( t + \pi ) = \frac { 7 } { 8 }$
B) $\cos ( t + \pi ) = - \frac { 8 } { 7 }$
C) $\cos ( t + \pi ) = \infty$
D) $\cos ( t + \pi ) = \frac { 8 } { 7 }$
E) $\cos ( t + \pi ) = - \frac { 7 } { 8 }$