I am having some trouble with these questions 1) Find all the critical points of f (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 2) Find an equation of the tangent plane to the surface of x^3 + y^3 - z^2 = 3 x y at (1, 2, 3) 3) Find an equation of the tangent plane to the surface of z= 3x^4 - 2 y^3 + 5 when x = 2 and y = 5