Find the Partial Derivative $f_{x}(9,-9)$ When $f(x, y)=7 x^{2}-9 x y$
A) 45
B) -45
C) -162
D) 207

Find the partial derivative.
-Find $f_{x}(9,-9)$ when $f(x, y) =7 x^{2}-9 x y$ .

A) 45
B) -45
C) -162
D) 207