According to the old saying, sine is the ratio of strands to chords.

The "string" in the ancient "hook three strands, four strings and five" is the hypotenuse in the right triangle. The thigh is long, and the ancients called the right side in the middle of a right triangle a "strand". A right triangle should be placed upright.

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 calculation formula:

Sine is equal to the division chord length (that is, diameter) of the section chief.

According to modern theory, sine is the ratio of the opposite side to the hypotenuse of a right triangle.

The modern sine formula is

Sin(a) = The opposite side of a right triangle is larger than the hypotenuse.

Put it in a circle, the hypotenuse R is the radius, the opposite side Y is parallel to the Y direction, and the adjacent side X is parallel to the X direction.

The angle α between the hypotenuse and the adjacent edge.

sin(a) = y / r

Regardless of y>x or y < =x

Whether a is big or small.