To determine the equation of the midline of a graph, we typically analyze the vertical behavior of the graph's waveform (often a sine or cosine function).

The midline of a periodic function represents the horizontal line that runs directly through the middle of the maximum and minimum values of the graph. It can be found by averaging the maximum and minimum values of the function.

Steps to find the midline equation:

1. Identify the maximum value (yₘₐₓ) of the graph.
2. Identify the minimum value (yₘᵢₙ) of the graph.
3. The equation of the midline is the average of these values: $y = \frac{yₘₐₓ + yₘᵢₙ}{2}$

If you can provide more specific details about the graph (e.g., a description of its amplitude, maximum and minimum points) or upload an image of the graph, I can assist with finding the exact midline equation.

Let me know if you'd like further explanation or help! Here are some related questions:

1. How do you find the amplitude of a sine or cosine graph?
2. What is the period of a trigonometric function and how is it determined?
3. How do phase shifts affect the equation of a periodic function?
4. Can we shift the midline of a function vertically? If so, how?
5. How do you express a trigonometric function with both amplitude and midline shifts?

Tip: The midline helps define the average behavior of a periodic function and is useful when analyzing oscillatory data, such as sound waves or tides.