8. Let the set $A=\{1,2\}$, the number of mappings $f$ from $A$ to $A$ that satisfy $f(f(x))=f(x)$ is $\qquad$.


8. 3. (1) $f: 1 \rightarrow 1,2 \rightarrow 2$;
(2) $f: 1 \rightarrow 1,2 \rightarrow 1$;
(3) $f: 1 \rightarrow 2,2 \rightarrow 2$.