- $ D = \\\mathbb{R}$.
- $ D = \\\left[ {\\\frac{2}{3}; + \\\infty } \\\right)$.
- $ D = \\\left( {\\\frac{2}{3}; + \\\infty } \\\right)$.
- $ D = R\\\backslash \\\left\\\{ {\\\frac{2}{3}} \\\right\\\}$.