Answer
$${f_{xx}}\left( {1,0} \right) - {f_{xx}}\left( {3,2} \right) = 0$$
Work Step by Step
$$\eqalign{
& f\left( {x,y} \right) = 4x + 5y - 6xy \cr
& {\text{Find }}{f_x} \cr
& {f_x} = {f_x}\left( {x,y} \right) = \frac{\partial }{{\partial x}}\left[ {4x + 5y - 6xy} \right] \cr
& {\text{Consider }}y{\text{ as a constant}} \cr
& {f_x} = 4\left( 1 \right) + 5\left( 0 \right) - 6\left( 1 \right)y \cr
& {f_x} = 4 - 6y \cr
& \cr
& {\text{Find }}{f_{xx}} \cr
& {f_{xx}} = \frac{\partial }{{\partial x}}\left[ {{f_x}} \right] \cr
& {f_{xx}} = \frac{\partial }{{\partial x}}\left[ {4 - 6y} \right] \cr
& {f_{xx}} = 0 \cr
& \cr
& {\text{Calculate }}{f_{xx}}\left( {1,0} \right) - {\text{ }}{f_{xx}}\left( {3,2} \right) \cr
& {f_{xx}}\left( {1,0} \right) = 0 \cr
& {f_{xx}}\left( {3,2} \right) = 0 \cr
& {f_{xx}}\left( {1,0} \right) - {f_{xx}}\left( {3,2} \right) = 0 \cr} $$
