In trigonometry, how is sine defined?

Sine is defined in the context of a right triangle as the ratio of the length of the side opposite the angle to the length of the hypotenuse. In this definition, the opposite side is the one that is directly opposite the angle of interest, while the hypotenuse is the longest side of the triangle, which is always opposite the right angle.

This fundamental definition of sine is a cornerstone of trigonometry, allowing for the analysis of various properties of triangles and periodic phenomena. It is especially useful in solving equations involving angles, distances, and heights, as well as in applications across physics and engineering. The correct option reflects this established relationship in a right triangle, demonstrating an understanding of basic trigonometric ratios.