2.23. Cartesian Equation For A General Conic
Eq(2.22) can be written as
. Taking the square of (2.29) gives
Note that the discriminant
so that eq(2.32) represents an ellipse,
parabola, or hyperbola if D is
negative, zero or positive, respectively.
[Caution: our D is the
negative of that given in the text].