Cos means cosine, the ratio of the right-angled side adjacent to the acute angle to the hypotenuse.
Sin means sine, corresponding to the edge of acute angle and the edge of hypotenuse.
Extended data:
In a right triangle, when the connecting lines AB, AC and BC of three points A, B and C on the plane form a right triangle, where ∠ACB is a right angle. For ∠BAC, for the opposite) a=BC, hypotenuse) c=AB, and adjacent) b=AC, there is the following relationship:
The concepts of sine and cosine in trigonometry were first introduced by Indian mathematicians, who also made sine tables more accurate than Ptolemy.
As we already know, the chord table created by Ptolemy and Hipparchus is a circular full chord table, which corresponds to arcs and chords sandwiched between arcs. Unlike Indian mathematicians, they correspond the half chord (AC) to the half arc (AD) of the whole chord, that is, AC corresponds to ∠AOC. In this way, they created a sine table instead of a full chord table.
Indians call the chord (AB) connecting the two ends of the arc (AB) "jiba", which means bowstring; One half (AC) of AB is called "Al Hajiwa". Later, when the word "Jiwa" was translated into Arabic, it was misunderstood as "bend" and "concave", and Arabic was "dschaib". /kloc-in the 0/2nd century, Arabic was translated into Latin, and the word was translated into "dou".
References:
Trigonometric Function-Baidu Encyclopedia