I am having some trouble with these questions

1) Find an equation of the tangent plane to the surface of x"3 + y"3 - z"2 = 3 x y at (1, 2, J3) 2) Find an equation of the tangent plane to the surface of 2: 3x"4 - 2 - y"3 + 5 when x = 2 and y = 5 3) Find all the critical points off (x,y) = x"3 - 3x"2 + 6y"2 +2 and f (x,y) = x"2 + xy + y"2 -10x -8y+5 then state if the points are relative maximum, relative minimum, or saddle points using second derivative test