A rational function is defined for all real values of the independent variable except those values for which the denominator of the function would be zero. So set the denominator equal to zero and solve the quadratic. If you have two distinct real zeros, then you have two values to exclude from the domain. If you have a perfect square trinomial and therefore one root with a multiplicity of two, you have one value to exclude. If the roots of the denominator quadratic are complex, then you have no real values to exclude and the domain of the function would be all real numbers.
Having said all of that, a quick glance at the signs in your quadratic denominator tell me that there are two real and distinct roots. Super Double Plus Extra Credit if you can tell me why.
John
My calculator said it, I believe it, that settles it
