Final answer:
Without the specific function, it's an educated guess to say the horizontal tangent line is at x = π/2 for common trigonometric functions like sine, as this is where its slope is zero.
Step-by-step explanation:
The question is asking us to find all values of x where the tangent line is horizontal. A horizontal tangent line occurs where the derivative of a function is zero because the slope of a horizontal line is zero. If we're dealing with a trigonometric function like sine or cosine, a horizontal tangent typically occurs at the maximum and minimum points of the function.
To determine the correct answer, we need the specific function in question, which is not provided. However, if we're assuming a common function like y = sin(x) or y = cos(x), the horizontal tangents occur at multiples of π/2 where the sine function is at its peak or valley, which would correspond to x = π/2 and x = 3π/2 for a sine curve, or x = 0 and x = π for a cosine curve.
Therefore, based on the assumption above, the correct answer is likely B. x = π/2, however, without the specific function provided, this is simply an educated guess based on common trigonometric functions.