question:Find the tangent plane that is horizontal to the surface Q: . Hint this is the lowest point on the surface

work: I get the partial derivatives and . I then equate them with zero and from I get x=0 and from I get z=y-1/3

The formula of the tangent plane is and solving for y I get So now I'm stuck because I was thinking I could plug this into my original equation but I can't since I have two possibilities.