The document discusses finding the gradient of implicitly defined curves using implicit differentiation. It provides the example curve x^3 + y^3 + x^2 - y = 0, which cannot be written explicitly as y = f(x) or x = f(y). To find the gradient at any point on an implicitly defined curve, the technique of implicit differentiation is used. The document then poses the question of finding the equation of the tangent line to the implicitly defined circle x^2 + y^2 - 6x + 2y - 3 = 0 at the point (1, 2).