Answer
$\theta=\arccos(\frac{5\sqrt 221}{221})$
Work Step by Step
We are given: $u=(2,3)\\
v=(4,-1)$ in $R^2$
Let $\theta$ be the angle between $u$ and $v$.
We obtain:
$$\cos \theta=\frac{}{||u||.||v||}\\
=\frac{2.4+3.(-1)}{\sqrt 2^2+3^2.\sqrt x4^2+(-1)^2}\\
=\frac{5}{\sqrt 221}$$
$$\rightarrow \theta=\arccos(\frac{5\sqrt 221}{221})$$
