Final answer:
The function that represents the ratio of the opposite side to the hypotenuse in a right triangle is the sine function. Therefore correct option is A
Step-by-step explanation:
The function that is equal to the ratio of the side opposite a given angle to the hypotenuse in a right triangle is the sine function. Considering a right triangle with an angle θ, the hypotenuse (often represented as h), the side opposite the angle (y), and the side adjacent to the angle (x), the sine of angle θ is calculated as sin(θ) = y/h. This is one of the basic trigonometric ratios and is fundamental in trigonometry.