Return null in FK

Hi,

I've a formula with where I want represent an IF THEN ELSE and in the ELSE I want to return a null or empty value:

The formula would be something like this:

(RATIO1 == 1) * (RATIO2 / RATIO3) + (RATIO1 == 0) * NULL

I mean, in case RATIO1 would be 0 I don't want make any opertion and in analysis for excel it should be ''.

Can anybody help me?

Thanks in advance.

Regards.