9. Consider the surface x a. Find the equation of the tangent plane to this surface at the point (1.2.2]) b. Find a point at which the tangent plane to this surface is horizontal. Are there any other such points? c. Find a point at which the tangent plane to this surface is vertical. Are there any other such points? 3. Compute the scalar surface integral xzdS for the surface S described by x + y = 1, 0 z 1, and x 0. Hint: [cos0d0 = sin 15 sin 30.