3. Intersections of two conics
3.1. Representation by symmetric matrices. We regard each of the two equations
C1 and C2 as defining a conic in the plane of triangle ABC. The question is there-
fore finding the intersections of two conics. This is done by choosing a suitable
combination of the two conics which degenerates into a pair of straight lines. To
do this, we represent the two conics by symmetric 3 x3 matrices