3. What is the domain of the following real valued function? $$f ( x ) = \log _ { 2 } \left( x ^ { 2 } - 5 x + 6 \right)$$ (a) $( - \infty , 2 )$\\ (b) $( 3 , \infty )$\\ (c) $( - \infty , 2 ) \cup ( 3 , \infty )$\\ (d) $( - \infty , \infty )$\\