\[\boxed{\text{1017\ (1017).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ 2x - 5,\ \ \frac{1}{2x - 5},\ \ \]
\[\sqrt{2x - 5},\]
\[1)\ 2x - 5 \Longrightarrow x - любое\ число;\]
\[2)\ 2x - 5 \neq 0 \Longrightarrow x \neq 2,5;\]
\[3)\ 2x - 5 \geq 0 \Longrightarrow x \geq 2,5.\]
\[\textbf{б)}\ 2x² + 7x - 4,\ \ \]
\[\frac{1}{2x^{2} + 7x - 4},\ \ \]
\[\sqrt{\frac{1}{2x^{2} + 7x - 4}},\]
\[1)\ 2x² + 7x - 4 \Longrightarrow x - любое\ \]
\[число;\]
\[2)\ 2x² + 7x - 4 \neq 0\]
\[D = 49 + 32 = 81,\]
\[x_{1} = \frac{- 7 + 9}{4} = 0,5,\ \ \]
\[x_{2} = \frac{- 7 - 9}{4} = - 4,\]
\[x \neq 0,5;\ \ \ x \neq - 4.\]
\[3)\ 2x² + 7x - 4 > 0\]
\[x_{1} = 0,5;\ \ \ \ x_{2} = - 4,\]
\[x \in ( - \infty;\ - 4) \cup (0,5; + \infty).\]
\[\textbf{в)}\ x² + 1,\ \ \sqrt{x^{2} + 1},\]
\[\ \frac{1}{x² + 1},\ \]
\[1)\ x² + 1 \Longrightarrow x - любое\ число.\]
\[2)\ x² + 1 \geq 0\]
\[x^{2} \geq - 1 \Longrightarrow x - любое\ число.\]
\[3)\ x² + 1 \neq 0\]
\[x² \neq - 1 \Longrightarrow x - любое\ число.\]