8. Set $A=\{(x, y) \mid y=a x+1, x, y \in \mathbf{R}\}, B=\{(x, y) \mid y=| x |$, $x, y \in \mathbf{R}\}$, and $A \cap B$ is a singleton set, the range of real number $a$ is $\qquad$
8. $(-\infty,-1] \cup[1,+\infty)$. Drawing the two curves in the same coordinate system will suffice.