Use the Definition of Partial Derivatives as Limits to Find $f _ { x } ( x , y )$

Multiple Choice

Use the definition of partial derivatives as limits to find $f _ { x } ( x , y )$ if $f ( x , y ) = 5 x ^ { 2 } - 9 x y + 2 y ^ { 2 }$ .

A) $5 y - 9 x$
B) $10 x - 9 y$
C) $10 x - 9$
D) $10 x - 9 x y$
E) $5 x - 9 y$