Using interpolating functions in Mathematica

[fuzzyfunnel]

I have an interpolating function in mathematica and just want to find when it takes a certain value, seems simple, but I can't do it.

i.e. I solved an equation numerically for z(rho) and got interpolating function x for z.

Now I want to know for which value of rho, z(rho)=1 for example.

Anyone know how?

 

[Dale]

Use FindRoot