Parallelogram definition
A parallelogram is a quadrilateral that has two pairs of parallel sides.
The parallelogram has vertices at the points $\vc{a},ドル $\vc{b},ドル $\vc{c},ドル and $\vc{d}$. We say it is spanned by the vectors $\vc{u}$ and $\vc{v}$. The point $\vc{e}$ is the midpoint between $\vc{a}$ and $\vc{d}$ as well as the midpoint between $\vc{b}$ and $\vc{c}$.