Find the projection of \vec{u} = \left [ \begin{matrix} -3 \\ 1 \end{matrix} \right ] onto the unit vector \vec{v} = \left [ \begin{matrix} 1/\sqrt{2} \\ 1/\sqrt{2} \end{matrix} \right ].
Find the projection of \vec{u} = \left [ \begin{matrix} -3 \\ 1 \end{matrix} \right ] onto the unit vector \vec{v} = \left [ \begin{matrix} 1/\sqrt{2} \\ 1/\sqrt{2} \end{matrix} \right ].
We have
proj_{\vec{v} }(\vec{u} ) = (\vec{v}\cdot \vec{u} )\vec{v}= \left(\frac{-3}{\sqrt{2} } + \frac{1}{\sqrt{2} } \right) \left [ \begin{matrix} 1/\sqrt{2} \\ 1/\sqrt{2} \end{matrix} \right ]
= \frac{-2}{\sqrt{2} } \left [ \begin{matrix} 1/\sqrt{2} \\ 1/\sqrt{2} \end{matrix} \right ]
= \left [ \begin{matrix} -1 \\ -1 \end{matrix} \right ]