\[\frac{1}{x + 3} - \frac{1}{x + 4} = \frac{1}{x + 7}\text{\ \ }\]
\[x \neq - 3;x \neq - 4;x \neq - 7\]
\[x + 7 = x^{2} + 7x + 12\]
\[x^{2} + 6x + 5 = 0\]
\[D_{1} = 9 - 5 = 4\]
\[x_{1} = - 3 + 2 = - 1;\ \]
\[x_{2} = - 3 - 2 = - 5.\]
\[Ответ:x = - 1.\]