The left figure shows that [math]w=u+v[/math]. The right figure shows that [math]Mw=Mu+Mv[/math]. Together they show that that (algebraically) [math]M(u+v)=Mw=Mu+Mv[/math]. [br][br]Geometrically, this means that a parallelogram is transformed to a (possibly collapsed) parallelogram.