Compute the Derivative Function $f ^ { \prime } ( x )$

Multiple Choice

Compute the derivative function $f ^ { \prime } ( x )$ algebraically.
$f ( x ) = x ^ { 2 } - 9$

A) $f ^ { \prime } ( x ) = 2 x ^ { 2 }$
B) $f ^ { \prime } ( x ) = 2$
C) $f ^ { \prime } ( x ) = x - 9$
D) $f ^ { \prime } ( x ) = 2 x - 9$
E) $f ^ { \prime } ( x ) = 2 x$