F = -(P/d^3)*x^2*y^2*(3*d-2*y)

partial^2 F/partial y^2 = (12*x^2*y-6*d*x^2)*P/d^3

partial^2 F/partial x^2 = (4*y^3-6*d*y^2)*P/d^3

partial F/partial x = (4*x*y^3-6*d*x*y^2)*P/d^3 partial^2 F/partial x partial y = (12*x*y^2-12*d*x*y)*P/d^3