Consider the ellipsoid 2x + y + 3z = 21. Find all the points where the tangent plane to this ellipsoid is parallel to the plane 4x+6z = 0. Hint: (-2*sqrt(28)/3,sqrt(28)/6,2*sqrt(28)), (2*sqrt(28)/3,-sqrt(: (If there are several points, separate them by commas.) Hint: The normal vectors of the tangent plane and the given plane must be parallel, and the point must actually lie on the ellipsoid. This should give you four equations in four unknowns that you can solve.