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bonjour,

(BC)//(DE)
→thalès
AC/AE = AB/DE = CB/DE
3/5,25 = AB/3,5
AB*5,25 = 3*3,5
AB = (3*3,5)/5,25 = 2cm

(AC)//(DE) si BA/BD = BC/BF
BA/BD = 2/5,5 = 4/11
BC/BF = 4/11

BA/BD = BC/BF → (AC)//(DE)

(bc)//(DE) le théorème de thales ac/AE =ab/ de = CB/ de 3/5,2,5=ab/3,5 ab*5,25=3* 3.5 ab =( 3*3,5)/5,25 = 2 cm (ac)//(DE) si ba/BD = bc/bf ba/BD = 2 /5,5=4/11 bc/bf = 4/11 ba /BD =bc /bf -> (ac)//(DE )