Kind of a bad thing to say about the UK isn't it?

Given point and [tex]P= (x_0, y_0, z_0)[/itex] then is a vector from the center of the sphere to C and so is normal to the sphere and a tangent plane at C. That means that we can write the equation of the plane as . Now, you say that M is a point on that tangent plane and it "coordinates" are known. But to give 3D coordinates, we would have to know what the coordinate system on that planeis and how it is connected to the three dimensional coordinate system.