3. The function $f(x)$ takes each value no more than twice. Moreover, for any non-zero $x$, the equality $f(x)+f(1-x)+f\left(\frac{1}{x}\right)=6$ holds. Find such an $x$, not equal to $\frac{5}{7}$, that $f(x)=f\left(\frac{5}{7}\right)$. If such an $x$ does not exist, write "no".