12. As shown in Figure $4, \odot C$ passes through the origin and intersects the coordinate axes at points $A$ and $D$ respectively. It is known that $\angle O B A=30^{\circ}$, and the coordinates of point $D$ are $(0,2)$. Then the coordinates of points $A$ and $C$ are $\qquad$
$\qquad$
12. $\left(-\frac{2 \sqrt{3}}{3}, 0\right) \quad\left(-\frac{\sqrt{3}}{3}, 1\right)$