ext{proj}_{\mathbf{c}} \mathbf{v} = rac{-3}{6} egin{pmatrix} 1 \ 2 \ -1 \end{pmatrix} = - rac{1}{2} egin{pmatrix} 1 \ 2 \ -1 \end{pmatrix} = egin{pmatrix} -0.5 \ -1 \ 0.5 \end{pmatrix}