It is worthy of notice that **Apollonius** nowhere introduces the notion of directrix for a conic, and that, though he incidentally discovered the focus of an ellipse and hyperbola, he did not discover the focus of a parabola. Conspicuous in his geometry is also the absence of technical terms and symbols, which renders the proofs long and cumbrous.

Create and save customized word lists. Sign up today and start improving your vocabulary!