T 7 4. [10 pts] For polar coordinates x=rcos and y=r sin 0, we get the partial derivative ar = cos . We also have r = 12 +y?, 50 x = V2 - y2 = (y2 - y2) 1/2 r 1 1 Then (r2 - y2)-1/2(2) = 2 r That means we get = cose and Which is correct? ar Explain how we get two different answers for the same partial derivative r 2 roos cos 1 r cos 5. [10 pts) Find all points on the surface 3x + 4y2 + ( + 6) = 32 at which the surface does not have a tangent plane