If the point on the sphere is x1,y1,z1, and the center of the sphere is x0.y0.z0

the tangent plane is (x-x1)(x1-x0)+(y-y1)(y1-y0)+(z-z1)(z1-z0)=0

the tangent plane is (x-x1)(x1-x0)+(y-y1)(y1-y0