[Math] What does the secant value represent

calculusgeometry

What does the secant value represent?

I know that $$\sec = 1/\cos(\theta)$$ but really I do not know what this value represents, so I need your help. A clear example with images would be appreciated.

Best Answer

In this image, notice that as $\theta$ grows from $0$ to a right angle, the segment labeled $\sec\theta$ grows from $1$ to $+\infty$, and if $\theta$ were to go from $0$ down to minus a right angle, $\sec\theta$ would also go from $1$ up to $+\infty$.

On the other hand $\tan\theta$ would go from $0$ (not $1$) to $+\infty$ in one case, and from $0$ down to $-\infty$ in the other case.

Notice that the tangent is the length of a segment that is tangent (touching but not crossing) to the circle and the secant is the length of a segment that is secant to (cutting across) the circle. The words come from the Latin words tangere and secare, meaning to touch and to cut.

(The second image treats the three "co-" functions. I drew these with xfig several years ago and uploaded them to Wikipedia, where they are seen in this article.)

Some trigonometric functions

Here's an image treating the three "co-" functions