Răspuns :
__M____N____P____Q
MN + PM =MQ
DE UNDE MN=PN=PQ
QP+NQ=MQ ⇒ MN +PM +QP+NQ =2MQ
Daca M, N, P si Q sunt 4 puncte necoliniare in plan, atunci:
MN + PM + QP + NQ = NM + MP + PQ + QN = NP + PN = 2 NP.
MN + PM + QP + NQ = NM + MP + PQ + QN = NP + PN = 2 NP.