Answer
$98.6^\circ$.
Work Step by Step
From what we learned: $\cos\theta=\frac{U\cdot V}{|U||V|}=\frac{5\cdot(-4)+12\cdot1}{\sqrt{5^2+12^2}\sqrt{(-4)^2+1^2}}=\frac{-8}{\sqrt{169}\cdot\sqrt{17}}=\frac{-8}{13\sqrt{17}}$
Thus $\theta=\cos^{-1}\frac{-8}{13\sqrt{17}}\approx98.6^\circ$.