39-41 Use polar coordinates to find the limit. [If (r, 0) are polar coordinates of the point (x, y) with r = 0, note that r - 0 as (x, y) -> (0, 0).] x3 + y3 39. lim (x, y) - (0, 0) x2 + )2 40. lim (x2 + y?) In(x2 + y2) (x, y) - (0, 0)