Trigonometry, Anatomy, Math History Trivia

Trigonometry and Anatomy have an etymological connection. This math lesson plan shows the strange word development of 'sine'.

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Trigonometry, Anatomy, Math History Trivia

(Published in Directory : Mathematics)

You would never expect to find a connection between the fields of trigonometry and anatomy, but you can assure your students: that connection is there!

It's actually an etymological connection, and your students may find it both interesting and amusing to learn the history of the word 'sine'.

It began with the Hindus, who used the word 'ardhajya' for sine. This word means 'half chord'. Why? That's a good question to explore with your students. If you draw a unit circle, a chord, and segments connecting the center to the midpoint and endpoint of the chord, then the sine of the angle created by these segments is equal to half of the length of the chord.

So the Hindus called it 'ardhajya'. This word was transliterated (not translated) and shortened into Arabic as 'jyb'.

Along come the Europeans who think that this is actually the Arabic word 'jayb' which means 'a gulf, a hole, or a pocket'.

Where did it go from here? It was translated (not transliterated) into Latin as 'sinus'.

That's right. When you write sin(45), what you really mean is the sinus of 45 degrees.

Of course, this allows the witty math teacher to then tell his students 'It's time to study our sinuses now.'

It's amazing how a silly little word history like that can relieve a little bit of the tension students naturally feel when studying an intimidating subject like trigonometry.

Source: An Introduction To The History Of Mathematics by Howard Eves

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