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The origins of Trigonometry
By Tom Read (T1386) on Thursday, December 9, 1999 - 05:06 pm:

I understand that trig was developed by the Romans as harbour defence theory. Sine comes from 'sinus' - Latin for passageway, cosine from 'corresponding' ie the outward distance corresponding to the sine. Sine is then the length from the end of the outward cos length to the passageway between the end of the sine and the shoreline. The hypotenuse is deemed to be 1. (Hence was sin2 + cos2 = 1).

I need to sharpen up my account and reasoning of all this in order to interest and convince my students. Can anybody tell me the full accurate story or point me towards a website that can? I suppose tan, sec, cosec and cot will all have physical significance in there, which justify the names they have been given? (I think tan is at right-angles from the hypotenuse, and hence tangent to the circle of which the hyp is the radius).

Any help greatly appreciated.

Tom Read

By Alex Barnard (Agb21) on Friday, December 10, 1999 - 10:55 am:

Try the following sites (I can't fully see all due to not having Java set up correctly - but even then they look like what you are seeking).

Short Trigonometry Course
Etymology of Trigonometry Names
The Trigonometrical Functions

AlexB.