BdMO Online Forum

Posted: **Tue Mar 21, 2017 9:26 pm**

Find all functions $f:Q \rightarrow Q$ such that
\[f(1)=2\]
and
\[f(xy)=f(x)f(y)−f(x+y)+1\]

Posted: **Thu Mar 23, 2017 12:27 am**

This can be solved by the basic arguments used to solve Cauchy's FE over Q. Try it yourself!

Hint if you're extremely desperate:

f(x)=?