Sine is a mathematical term. In a right triangle, the ratio of the opposite side to the hypotenuse of any acute angle ∠A is called the sine of ∠A, which is abbreviated from the English word sine, that is, the opposite side/hypotenuse of Sina = ∠ A. In ancient times, sine was the ratio of chords to chords.

Cosine (cosine function), a kind of trigonometric function. In Rt△ABC (right triangle), ∠ C = 90, and ∠A's cosine is the hypotenuse of its adjacent side than the triangle, that is, cosA=b/c, which can also be written as cosa=AC/AB. Cosine function: f(x)=cosx(x∈R).

R&D:

As early as the 2nd century AD, the ancient Greek astronomer Ptolemy knew the sine theorem, and so did the famous Arab astronomer Al biruni in the Middle Ages. However, it was the Arab mathematician and astronomer Nassir al-Ahldin who explicitly proposed and proved this theorem for the first time in the13rd century. In Europe, the Jewish mathematician Gehlsen stated this theorem with sine, chord and arc, but he did not give a clear proof.

/kloc-In the 5th century, the German mathematician Rejo Montanus gave the sine theorem in On Various Triangles, but simplified Nasir-Ud-deen's proof. 157 1 year, the French mathematician F. viete (1540-1603) proved the sine theorem in his Mathematical Law with a new method. Later, the German mathematician Bi Tix proved the sine theorem by Vedic method in his trigonometry? .