The denominator must be different than zero.
Therefore
[tex](x + 11)(x-5)\neq0\iff x+11\neq0\ \wedge\ x-5\neq0\\\\x\neq-11\ wedge\ x\neq5[/tex]
The domain is the set of all real numbers except -11 and 5
[tex]D=\mathbb{R}-\{-11,\ 5\}[/tex]
