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in triunghiul ABC ,consider punctele D € AB si E € AB ,astfel ASTFEL A € (DB) si A € (EC). Aratati ca DE||BC,daca:
a) AD=3 cm,BD=15CM,AE=3CM SI EC=15CM
b)AD=9CM,BD=6CM,CE=9CM SI AC-15CM
c)BD=7CM,AB=21CM,AE=8CM SI AC=12CM