+y d(xy) x-y when x y then 19+1 0, otherwise (a) (b) (c) (d) is discontinuous and both partial derivatives exists at (0, 0) continuous and both partial derivati

+y d(xy) x-y when x y then 19+1 0, otherwise (A) (B) (C) (D) is discontinuous and both partial derivatives exists at (0, 0) continuous and both partial derivatives exists at (0, 0) discontinuous and both partial derivatives and not exists at (0, 0) o continuous and both partial derivatives does not exists at (0, 0)