9. Let the function $f_{0}(x)=|x|, f_{1}(x)=\left|f_{0}(x)-1\right|, f_{2}(x)=\left|f_{1}(x)-2\right|$, then the area of the closed part of the figure enclosed by the graph of the function $f_{2}(x)$ and the $x$-axis is $\qquad$
Answer:
As shown in the figure, the area of each small triangle is 1, so the area of the closed part formed by the graph of the function $f_{2}(x)$ and the $x$-axis is 7.