Let $f ( x ) = \operatorname { coth } ( 3 x )$

Multiple Choice

Let $f ( x ) = \operatorname { coth } ( 3 x )$ Then $f ^ { \prime } ( x )$ is

A) $3 \operatorname { csch } ^ { 2 } ( 3 x )$
B) $- 3 \operatorname { csch } ^ { 2 } ( x )$
C) $3 \operatorname { csch } ^ { 2 } ( x )$
D) $- 3 \operatorname { coth } ^ { 2 } ( 3 x )$
E) $- 3 \operatorname { csch } ^ { 2 } ( 3 x )$