TITLE: Why are the trig functions versine, haversine, exsecant, etc, rarely used in modern mathematics?
QUESTION [45 upvotes]: I was browsing through a Wikipedia article about the trigonometric identities, when I came across something that caught my attention, namely forgotten trigonometric functions.
The versine (arguably the most basic of the functions), coversine, haversine and exsecant formulas had once been utilised for navigational purposes, prior to GPS tracking systems. However, recently, they have become less common in modern mathematics and beyond. Why is that?
Here is a link to a PDF file describing all of these now-obsolete trig functions: 

The Forgotten Trigonometric Functions, or
How Trigonometry was used in the Ancient Art of Navigation (Before GPS!)

REPLY [2 votes]: Historically, those oddball functions were used primarily in navigation to reduce sextant readings and times to latitude and longitude.   With the advent of radio, the need for that was greatly reduced, as we have radio direction finding, loran, and, more recently, GPS.