noun, plural di·rec·trix·es, di·rec·tri·ces [dih-rek-tri-seez, dahy-, dahy-rek-trahy-seez] /dɪˈrɛk trɪˌsiz, daɪ-, ˌdaɪ rɛkˈtraɪ siz/.
Origin of directrix
Examples from the Web for directrix
Historical Examples of directrix
As necessary as the directrix is to the curve, so are the corresponding laws to the State.
Directrix, a fixed line that is required for the description of a curve.The New Gresham Encyclopedia
Similarly, in an hyperbola a vertex is nearer 704 to the directrix than to the focus.
If a parabola roll on another parabola, their vertices coinciding, the focus of the first traces out the directrix of the second.
With your permission I will add a few words to those I have already uttered with regard to the directrix.