CRPE 2024. REMISE À NIVEAU. THEORÈME DE THALÈS. DÉMONSTRATION

If points A, B, and C on the one hand, and A, D, and E on the other, are aligned in this order, and lines (BD) and (CE) are parallel, then according to Thales's theorem, AB/AC = AD/AE = BD/CE CONVERSELY. If points A, B, and C on the one hand, and A, D, and E on the other, are aligned in this order, and lines AB/AC = AD/AE, then according to the converse of Thales's theorem, lines (BD) and (CE) are parallel.