Negative vector
A negative vector -v is a vector that has the same magnitude as a vector v but in the opposite direction.
Example
Given a vector v
$$ v = \begin{pmatrix} 2 \\ 1 \end{pmatrix} $$
The negative -v of the vector v is a vector obtained by the scalar product between -1 and the vector v
$$ -v = -1 \cdot v = -1 \cdot \begin{pmatrix} 2 \\ 1 \end{pmatrix} = \begin{pmatrix} -2 \\ -1 \end{pmatrix} $$
The negative vector -v in R2 has the same length but in the opposite direction.
