If a line parallel to one side of a triangle intersects the other two sides, then it divides the two sides proportionally. The converse is also true. In the image below, this tells us AD / DB = AE / EC.

# Triangle proportionality theorem

Geometry

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Geometry

If a line parallel to one side of a triangle intersects the other two sides, then it divides the two sides proportionally. The converse is also true. In the image below, this tells us AD / DB = AE / EC.