z = x sin(xy) + x^2 y^2 - 7 x

z'_x = sin(xy) + xy cos(xy) + 2 x y^2 - 7

z'_y = x^2 cos(xy) + 2 x^2 y

z'_xx = 2 y cos(xy) - x y^2 sin(xy) + 2 y^2

z'_xy = 2 x cos(xy) - x^2 y sin(xy) + 4 xy = z'_yx

z'_yy = -x^3 sin(xy) + 2 x^2