Răspuns:
a) XY + YZ + ZX = 0 ( vector la toate)
XY(vector) + YZ ( vector) = XZ ( vector)
XZ(vector) + ZX(vector) = XX(vector) = 0(vector)
-> XY(vector) + YZ(vector) + ZX(vector) = 0(vector)
b) MN + NP + PQ + QM = 0 ( vector la toate)
Grupam : MN( vector) + NP( vector) = MP ( vector) - regula triunghiului
PQ( vector) + QM(vector) = PM ( vector )
MP ( vector) + PM (vector) = MM ( vector) = 0
-> MN (vector) + NP (vector) + PQ ( vector) + QM(vector) = 0(vector)
Am folosit numai regula triunghiului!
