Pre-calculus Complex coordinate law of cosine help  
Let $\theta = \angle BAC$. Then we can write $\cos \theta = \dfrac{x}{\sqrt{2}}$
Find x.
Currently, that is all I have. I think I should use Law of cosine. Where should I progress?

$$a = BC = \sqrt{2^2+3^2}=\sqrt{13}$$
$$b = AC = \sqrt{3^2+1^2}=\sqrt{10}$$
$$c = AB = \sqrt{2^2+1^2}=\sqrt{5}$$
so $$\cos \theta = {b^2+c^2-a^2\over 2bc} = {1\over 5\sqrt{2}}\implies x=1/5$$
