Literally trigonometry does mean the measurement of angles^{1)}. Euler was the first
who defined (1749) the trigonometric functions as proportions of lines. He was also the one who
introduced the notation for these functions.
But long for the starting of the era scholars in the old Greece and in India where already
studying the trigonometric functions. In the Middle Ages (800 AD) the functions have been
studied intensively by Arab speaking mathematicians. All used the functions as
cords, it
took until the 18th century that the current view was adopted.
The basic trigonometric functions are:
Some more advanced trigonometric functions are :
notes
1) goonia (Gr.) = angle, metreoo (Gr.) = to measure
