\[\boxed{\text{1071.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ y = 4x - 8\]
\[x - любое\ число.\]
\[\textbf{б)}\ y = x² - 5x + 1\]
\[x - любое\ число.\]
\[\textbf{в)}\ y = \frac{2x}{5 - x}\]
\[5 - x \neq 0\]
\[x \neq 5\]
\[x \neq 5.\]
\[\textbf{г)}\ y = \frac{3}{(x - 4)(x + 1)}\]
\[(x - 4)(x + 1) \neq 0\]
\[x - 4 \neq 0\ \ \ \ и\ \ \ \ x + 1 \neq 0\]
\[x \neq 4\ \ \ \ \ \ \ \ \ \ \ и\ \ \ \ \ \ x \neq - 1\]
\[x \neq 4;\ x \neq - 1.\]
\[\textbf{д)}\ y = \frac{1}{x^{2} + 1}\]
\[x^{2} + 1 = 0\]
\[x^{2} = - 1 - нет\ решений.\]
\[x - любое\ число.\]
\[\textbf{е)}\ y = \sqrt{x - 5}\ \]
\[x - 5 \geq 0\]
\[x \geq 5.\]