$$\lim_{x \to \infty} \log{\left(\cos{\left(2 x \right)} \right)} = \log{\left(\left\langle -1, 1\right\rangle \right)}$$
$$\lim_{x \to 0^-} \log{\left(\cos{\left(2 x \right)} \right)} = 0$$
More at x→0 from the left$$\lim_{x \to 0^+} \log{\left(\cos{\left(2 x \right)} \right)} = 0$$
More at x→0 from the right$$\lim_{x \to 1^-} \log{\left(\cos{\left(2 x \right)} \right)} = \log{\left(- \cos{\left(2 \right)} \right)} + i \pi$$
More at x→1 from the left$$\lim_{x \to 1^+} \log{\left(\cos{\left(2 x \right)} \right)} = \log{\left(- \cos{\left(2 \right)} \right)} + i \pi$$
More at x→1 from the right$$\lim_{x \to -\infty} \log{\left(\cos{\left(2 x \right)} \right)} = \log{\left(\left\langle -1, 1\right\rangle \right)}$$
More at x→-oo