Several Properties of Quadratic Surface Tangent to Plane
This article has proved tangent-points have a common plane when quadratic surface is tangent to plane passing by the point outside quadratic surface , discussed several properties of quadratic surface tangent to plane.
A. L. Wang "Several Properties of Quadratic Surface Tangent to Plane", Advanced Materials Research, Vols. 108-111, pp. 1229-1234, 2010