8. The equation of the circle passing through the intersection points of the circles $x^{2}+y^{2}+4 x-4 y=0$ and $x^{2}+y^{2}-x=0$ and the point $(1,-1)$ is $\qquad$ .
8. $9 x^{2}+9 y^{2}-14 x+4 y=0$. Hint: The equation can be set as $x^{2}+y^{2}+4 x-4 y+\lambda\left(x^{2}+y^{2}-x\right)=0$, substitute $(1,-1)$, and solve to get $\lambda=-10$.