Final answer:
The midline for y = 2cos(x) - 1 is the line y = -1.
Step-by-step explanation:
The midline for the equation y = 2cos(x) - 1 is the horizontal line that represents the average value of the function. In this case, the midline is the line y = -1. The midline is important because it helps us understand the shifting and stretching of the graph of the cosine function.