Gaskin's theorem

Gaskin's theorem [′gas·kinz ‚thir·əm]

(mathematics)

A theorem in projective geometry which states that if a circle circumscribes a triangle which is identical with its conjugate triangle with respect to a given conic, then the tangent to the circle at either of its intersections with the director circle of the conic is perpendicular to the tangent to the director circle at the same intersection.