A Course of Pure Geometry

A₁ ABCD asymptotes B₁ bisectors C₁ C₂ called centre of similitude chord of contact circular points circumcentre circumcircle coaxal circles coaxal system collinear points common tangent concurrent concurrent lines confocal conic touching conjugate lines constant coplanar coplanar circles corresponding points cross-ratio curve cut the line diagonals directrix ellipse figure F fixed point focus four points given circles given point harmonic conjugates homographic imaginary incentre incircle inscribed inverse points involution limiting points line at infinity line joining locus meet middle point nine-points circle opposite sides orthocentre P(ABCD pairs of points parabola parallel pedal line perpendicular perspective plane points of contact points of intersection polar pole Prop Pure Geometry quadrangle quadrilateral radical axis radius range ratio rectangular hyperbola right angles self-conjugate Shew sides BC straight line student symmedian point system of coaxal tangents theorem three points triangle ABC vertex vertices