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- $ D = \\\mathbb{R}$.
- $ D = \\\mathbb{R}\\\backslash \\\{ 1\\\} .$
- $ D = \\\mathbb{R}\\\backslash \\\{ - 5\\\} .$
- $ D = \\\mathbb{R}\\\backslash \\\{ - 5;{\\\text{ }}1\\\} .$