salam
1) v(BC) = v(BI)+v(IJ)+v(JC) = 3.v(IJ) =====> 2.v(C'B') = 3.v(IJ)
I et J partagent [BC] en 3 parties égales
2) Thalès:
IJ / C'B' = KJ / KC' = 2/3
====> v(JK) = 2/3.v(KC')
====> v(JK) = 2/3.[v(KJ) + v(JC')]
====> 5/3.v(JK) = 2/3.v(JC')
====> v(JK) = 2/5.v(JC')
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