Origin of trig terms tangent and secant

By @GregLocock

tangent - Latin, tangere, to touch

secant - Latin secare - to cut

[That’s what Chambers 20th C says, anyway]

Euler pretty much nailed modern trig terminology in 1748. And you don’t argue with Euler.

Here’s a great diagram, showing why they are named that way:

And, here’s wiki’s take on history

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He was likely the father of Topology… the study of mathematical surfaces.


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I love that diagram of a circle of unit radius. It makes everything so clear and actually gives us a rough idea of approximately what size the various trig functions should be.