$\text { For } f ( x , y ) = \sin ( 7 x y ) \text {, evaluate } f _ { x } \text { at the point } \left( 2 , \frac { \pi } { 4 } \right)$

Multiple Choice

$\text { For } f ( x , y ) = \sin ( 7 x y ) \text {, evaluate } f _ { x } \text { at the point } \left( 2 , \frac { \pi } { 4 } \right)$

A) $f _ { x } \left( 2 , \frac { \pi } { 4 } \right) = \frac { 7 \pi } { 4 }$
B) $f _ { x } \left( 2 , \frac { \pi } { 4 } \right) = 0$
C) $f _ { x } \left( 2 , \frac { \pi } { 4 } \right) = 7$
D) $f _ { x } \left( 2 , \frac { \pi } { 4 } \right) = \frac { 7 \pi } { 2 }$
E) $f _ { x } \left( 2 , \frac { \pi } { 4 } \right) = 14$