If $\vec{a}$ ,$\vec{b}$ ,$\vec{c}$ ,$\vec{d}$ are the position vector of point $A,B,C$ and $D$ , respectively referred to the same origin $O$ such that no three of these point are collinear and $\vec{a}$ + $\vec{c}$ = $\vec{b}$ + $\vec{d}$ , than prove that quadrilateral $ABCD$ is a parallelogram.

Views: 796 students