6. (2001 National High School Competition) The length of the minor axis of the ellipse $\rho=\frac{1}{2-\cos \theta}$ is equal to

保留了源文本的换行和格式。
6. $\frac{2}{3} \sqrt{3} \cdot a+c=\rho(0)=1, a-c=\rho(\pi)=\frac{1}{3}$, so $a=\frac{2}{3}, c=\frac{1}{3}, b=\sqrt{a^{2}-c^{2}}=\frac{\sqrt{3}}{3}$, thus $2 b=\frac{2 \sqrt{3}}{3}$.