Definition: sin: In a right triangle, the ratio of the opposite side to the hypotenuse of ∠α (non-right angle) is called the sinα of ∠α, that is, the hook-chord ratio. The "string" in the ancient "hook three strands, four strings and five" is the hypotenuse in the right triangle. The thigh is a human thigh. The ancients called the long right side of a right triangle "thigh".
Relationship between angle functions
(sine) Sin θ = opposite side A/ oblique side c
(cosine) Cosθ = adjacent side B/ oblique side c
(tangent) Tanθ = opposite side A/ adjacent side b
Opposite side A = hypotenuse C * Sinθ
Opposite side A = adjacent side B * Tanθ
Adjacent side B = hypotenuse C * Cosθ
Adjacent side B = opposite side A/Tanθ.
Hypotenuse C = opposite side A/Sinθ
Oblique side C = adjacent side B/Cosθ