Exercise 2

Find the angle between each two, if it is defined.

• (a)  $\begin{pmatrix}1\\ 2\end{pmatrix},\begin{pmatrix}1\\ 4\end{pmatrix}$     (b)  $\begin{pmatrix}1\\ 2\\ 0\end{pmatrix},\begin{pmatrix}0\\ 4\\ 1\end{pmatrix}$     (c)  $\begin{pmatrix}1\\ 2\end{pmatrix},\begin{pmatrix}1\\ 4\\ -1\end{pmatrix}$