ABCD paralelogram
A(1,2), B(-2,2), C(-1,-3) si d(xD; yD)
Diagonalele paralelogramului se injumatatesc.
Notam M(xM; yM) punctul de intersectie al diagonalelor AC si BD
=> xM=(xA+xC)/2=(1-1)/2=0
yM=(yA+yC)/2=(2-3)/2=-1/2
dar xM=(xB+xD)/2=0
=> -2+xD=0; xD=2
yM=(yB+yD)/2=-1/2
=> 2+yD=-1
yD=-3
=> D(2; -3)
