Final answer:
The equation of the midline for the function y = -2 + 2sin(3x) is y = -2, which represents the average value of the sine function over one cycle and reflects the vertical shift of the function.
Step-by-step explanation:
The equation of the midline for y = -2 + 2sin(3x) is determined by the constant term and the vertical shift of the sinusoidal function representing the wave. In this case, the midline is a horizontal line that represents the average value of the function over one cycle of the sine wave. Since the sine function oscillates above and below the midline, and there is a vertical shift of -2 units in the given equation, the equation of the midline is y = -2.