Point 1 of 9 — Unit 3: Parallel Lines, Proportional Segments and Angle BisectorsQuestion bank: 0 questions (0 with pictures)
01 3-1 The line parallel to one side of a triangle
Theorem: a straight line drawn parallel to one side of a triangle, cutting the other two sides, divides them in the same ratio: if DE ∥ BC with D on AB and E on AC, thenAD/DB = AE/EC.
Equivalent forms that follow from it: AD/AB = AE/AC = DE/BC — which is the same as the similarity △ADE ~ △ABC.
Use the first form when the question involves the two parts of a side, and the second when it involves a whole side or the parallel segment itself.
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