Răspuns:
DE || BC => [tex]\frac{AD}{AB} = \frac{AE}{AC}[/tex] => [tex]\frac{2}{3} =\frac{AE}{21}[/tex] => AE = 7 x 2 => AE = 14 cm ( din Thales )
AE + EC = AC => EC = AC - AE = 21 - 14 = 7 cm
raspuns : A) 7 CM
( am zis AD/AB = 2/3 pt ca ni se spune ca AD = 2 DB iar AD + DB = AB
=> AB = 3DB dar AB = DB + AD => AD = 3DB - DB <=> AD = 2DB
iar AD/AB = 2DB/3DB = 2/3 )
