Why are sin, cos and tan called sin, cos and tan?
You probably know of the three main trigonometry functions — sine, cosine and tangent. You might also know of some extra trig functions called secant, cosecant and cotangent. And you might have seen that the inverse trig functions are sometimes referred to as arcsine, arccosine, etc.
But where do these names come from?
In this article, we will look at the origins of these names.
If you are not familiar with chords, tangents, and secants of a circle, take a look at the parts of a circle article.
Here is a related video: https://youtu.be/XuIeEMw_YYM
Primary trig functions — sine, tangent, secant
When we think about the main trig functions, we usually think of sine, cosine and tangent. Those are the functions that are most often used to solve trigonometry problems.
But historically the sine, tangent and secant functions were considered the primary functions.
Why is this? If we form a triangle inside a unit circle, with an angle a at the centre, then the sine, tangent and secant functions will tell us the lengths of each of the three sides in terms of a. Each function is named after the side it relates to.
