2. If $3 f(x-1993)+4 f(1993-x)$ $=5(x-1993)$, for all real numbers $x$, then the analytical expression of $f(x)$ is $\qquad$.
2. Solution Let $x-1993=t$. Then $x=1993+t$.

Thus, we have $3 f(t)+4 f(-t)=5 t$,
and $3 f(-t)+4 f(t)=-5 t$.
Solving (1) and (2) gives $f(t)=\frac{7}{5} t$.
That is, $f(x)=\frac{7}{5} x$.