Voltage controlled question

[jbv]

Let's imagine a perfect VCO expo converter.

For example, I perfectly understand that, if +1 V used as CV input gives
440 Hz, then +2V will
lead to 880 Hz.

But what about arbitrary input voltage ? I mean : which freq will I get
if I inject +1.2894 V,
or +4.0647 V, or whatever...

In other words : what is the math function that gives the output freq of
a VCO when we know
the value of CV input (and the VCO original tuning, of course) ?

I must confess that my math skills are somehow limited...

Thanx

jbv