I'm graphing this periodic function, it has the same min value for each for the two periods, but the max value is different for the two periods. Should I use the higher max value to work out the equation for the function, or should I average them?
In the absence of any other information about how the amplitude changes, I'd just use a linear rate of change.
For instance, y = (2+0.3x) sin(x)
Or, if you insist on a constant amplitude, then averaging them seems like a good option.