Let F ( x, y, z ) = x9 + z sin (x y z).
Then by the Implicit Function Theorem ∂z/∂x = - [ ∂F/∂x] / [∂F/∂z] and ∂z/∂y = - [ ∂F/∂y] / [∂F/∂z]
∂z/∂x = - [ ∂F/∂x] / [∂F/∂z]= [ 9 x8 +y z2 cos (x y z )] / [ x y z cos ( x y z) - sin (x y z) ] and
∂z/∂y = - [ ∂F/∂y] / [∂F/∂z] =[ x z2 cos ( x y z) ] / [ x y z cos ( x y z) - sin (x y z) ] .