\[\frac{x^{2} + 15x + 56}{x^{2} - 12x + 20} < 0\]
\[1)\ x^{2} + 15x + 56 =\]
\[= (x + 8)(x + 7)\]
\[x_{1} + x_{2} = - 15;\ \ \ x_{1} \cdot x_{2} = 56\]
\[x_{1} = - 7;\ \ \ x_{2} = - 8.\]
\[2)\ x^{2} - 12x + 20 =\]
\[= (x - 2)(x - 10)\]
\[x_{1} + x_{2} = 12;\ \ x_{1} \cdot x_{2} = 20\]
\[x_{1} = 10;\ \ \ x - 2 = 2.\]
\[\frac{(x + 8)(x + 7)}{(x - 2)(x - 10)} < 0\]
\[- 8 < x < - 7;\ \ 2 < x < 10.\]