According to the old saying, sine is the proportional pythagorean theorem between strands and chords.
The "string" in the ancient "hook three strands, four strings and five" is the hypotenuse of a right triangle. The thigh is long, and the ancients called the right side of the middle of a right triangle a "strand". The right triangle placed directly should be the thigh standing straight.
Sine is the ratio of strands to chords, and cosine is the ratio of remaining right angles to chords.
Sine is equal to the division length of the section chief.
Put the twisted rope in the circle. A chord is a line connecting two points on a circle. The largest string is the diameter. If the chord of a right triangle is placed on the diameter, it is a long chord, which is sine, and the hook is a short chord, which is cosine-cosine.
Sine is one of six acute trigonometric functions, and the other five are cosine (cos) and tangent (tan), cotangent (cot), secant (sec) and cotangent (csc).