Question: How do I plot a function versus a function.

I have two sets of scatter data.  Each set has been fit by a different function which is dependent on independent variable N.  The x-axis is 1/N. 

Set 1:

Scatter data is (0.125, -4.72557), (0.08333, -4.53944), (0.0625, -4.48229), (0.05, -4.42733)

where the x-axis is 1/N with N = 8, 12, 16, 20 and the y-axis is a function in terms of N as well: -8.55704612297018*SQRT(1-0.73962210555774*COS(PI()/(N+1)))

Set 2:

Scatter data is (0.125, -1.7312), (0.08333, -1.96658), (0.0625, -2.1274), (0.05, -2.187)

where the x-axis is 1/N with N = 8, 12, 16, 20 and the y-axis is a function in terms of N as well: -8.55704612297018*SQRT(1-0.73962210555774*COS(PI()/(N+1)))+10.112*(1/N)+1.7295

So, my problem is how to plot a function versus a function in both cases.  I wish to display both of these data sets with their fits on the same plot.