Amongst the “technical terms” that have come into use in connection with Coordinate Geometry, not the least convenient is the word Power. The only definition of a general kind for this term that I have met with is the following:

“Def.—The result of substituting the coordinates of any point in the equation of any line or curve is called the Power of that point with respect to the line or curve.

“[This definition, first given by Steiner, is now employed by all the French and German writers.]”