When is the $\text{cos}(x) =$ to $0$?

Logarithms have restrictive domains: $x$ cannot be less than or equal to $0$. What value(s) of $x$ will make $x^² + 1 ≤ 0$?

$D = (−∞, ∞)$

$x^² - x - 6 ≠ 0$

Both the numerator and the denominator have restricted domains. To find the domain of $k(x)$, all restrictions apply... combine the domains together.