7. (The 8th "Hope Cup" Senior High School Competition) $f(x)$ is a function defined on $(-\infty,+\infty)$, and it is an even function, with $f(1+x)=f(1-x)$. When $-1 \leqslant x \leqslant 0$, $f(x)=-\frac{1}{2} x$. Then $f(8.6)=$ $\qquad$ .
7. 0. 3. From the given conditions, $f(1+x)=f(1-x)=f(x-1)$, so $y=f(x)$ is a periodic function with a period of 2, and its graph can be drawn as shown in Figure 1-4.
Thus, $f(8.6)=f(-0.6)=-\frac{1}{2}(-0.6)=0.3$.