Find the Specified Quantity $y = - 2 \cos \left( 3 x + \frac { \pi } { 4 } \right)$

Multiple Choice

Find the specified quantity.
-Find the amplitude of $y = - 2 \cos \left( 3 x + \frac { \pi } { 4 } \right)$ .

A) $\frac { \pi } { 2 }$
B) 2
C) $- 6$
D) 3