When is the cos(x) = to 0?

Logarithms have restrictive domains: x cannot be less than or equal to 0. What value(s) of x will make x² + 1 ≤ 0?

D = (−∞, ∞)

x² - 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.