\[\boxed{\text{72\ (72).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\textbf{а)}\ \frac{3a}{2a + 25}\ \]
\[2a + 25 = 0\]
\[2a = - 25\]
\[a = - 12,5\]
\[Ответ:\ \ при\ a \neq - 12,5\]
\[\textbf{б)}\ \frac{2y}{9 + y^{2}}\]
\[9 + y^{2} = 0\]
\[y^{2} = - 9\]
\[y^{2}\ не\ может\ быть\ \]
\[отрицательным\ числом.\]
\[Ответ:при\ любых\ y.\]
\[\textbf{в)}\ \frac{5x}{3x \cdot (x + 12)}\]
\[3x \cdot (x + 12) = 0\]
\[3x = 0;\ \ \ \ x + 12 = 0\]
\[x = 0\ \ \ \ \ \ \ \ x = - 12\]
\[Ответ:при\ x \neq 0\ и\ x \neq - 12.\]
\[\textbf{г)}\ \frac{7a}{(a + 1) \cdot (a - 4)}\]
\[(a + 1) \cdot (a - 4) = 0\]
\[a + 1 = 0;\ \ \ \ \ a - 4 = 0\]
\[a = - 1\ \ \ \ \ \ \ \ \ \ \ a = 4.\]
\[Ответ:при\ a \neq - 1\ и\ a \neq 4.\]