# Inverse of a linear combination of two functions

I am interested in studying the behavior of the inverse of a linear combination of two functions as the parameter varies. My attempt is in the picture. Since my aim is to use Manipulate, I am trying to keep h (the parameter) explicit in InverseFunction, so that I will be able to make h vary. Unfortunately, when I try to plot the last line, I get an empty graph. How could I solve the problem?

f[x_]=x+2
g[x_]=x^2
h:=0.5
mix[x_]:=h f[x]+(1-h) g[x]

finv[y_]:=InverseFunction[f][y]
ginv[y_]:=InverseFunction[g][y]
mixinv[y_]:=InverseFunction[mix][y]

Plot[mixinv[y], {y, -5, 5}]
Plot[InverseFunction[h f[x] + (1-h) g[x]][y], {y, -5, 5}]


## 1 Answer

If you want h to be a manipulatable parameter, then make it a variable of your functions.

mix[x_, h_] := h f[x] + (1 - h) g[x]
mixinv[y_, h_] := InverseFunction[mix, 1, 2][y, h]


The syntax for the multi-argument form of InverseFunction says take the inverse with respect to the first argument, out of 2 total arguments.