Refresh my memory. Geometry

Silly Old Harry
Caught A Herring
Trawling Off America

Well, there’s still the problem that how many kids know the word “secant” in the other sense to begin with, and so on for “sine” and whatnot. :slight_smile:

(But I do agree that all the trigonometric functions are better taught via the unit circle than via magnitude ratios in right triangles; cosine and sine as X and Y coordinates, respectively, as one rotates counterclockwise from the right, tangent as the slope of the radius, etc. Much more clear what’s going on with the sign of the result and with negative, obtuse, or “improper” angles, much easier to explain where the differentiation rules come from, and so on. I’m just not sure that it would be particularly helpful to try and clarify “Wait, which one is sine and which one is cosine?” by drawing on non-existent prior memories of the terms being used in some previous fashion, or similarly of what a “secant” is in this context and why its length should happen to be the reciprocal of the cosine, and so on; when these come up, I still can’t see any better resort than to rote memorization: “Cosine is the X coordinate; Sine is the Y coordinate; Secant is 1/cosine…”.)