Which statement defines sine in trigonometry?

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Sine measures the vertical component of an angle’s rotation. In a right triangle, it’s the ratio of the opposite side to the hypotenuse, and on the unit circle it corresponds to the y-coordinate of the point reached by rotating by that angle. So describing the sine as “the sine of the angle” matches its role as the measure of that vertical component of rotation. The other options describe the other trig functions: cosine is the horizontal component, tangent is the ratio opposite to adjacent, and the reciprocal of cosine is secant. For example, if the opposite side is 3 and the hypotenuse is 5, sine is 3/5 = 0.6, illustrating this vertical component concept.