What is sine?

• A. The ratio of opposite over adjacent
• B. The sine of the angle of rotation
• C. The tangent of the angle of rotation
• D. The cosine of the angle

Answer: (B)

Sine is a function of an angle that gives a value tied to how a rotation projects onto a vertical component. In a right triangle, sine is defined as the length of the side opposite the angle divided by the hypotenuse, and on the unit circle it corresponds to the y-coordinate of the point reached by rotating by that angle. Describing sine as the sine of the angle emphasizes that it’s a value you get by applying the sine function to a specific angle, which is the essence of what sine represents. The other options describe tangent (opposite over adjacent) or cosine (adjacent over hypotenuse), so they mix up the definitions.