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# Parallel Lines & Proportional Parts

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Author: Kyle Webb

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Tutorial

## Triangle Proportionality Theorem & Converse

Theorem 6.4 Triangle Proportionality Theorem
If a line is parallel to one side of a triangle and intersects the other sides, it divides the two sides proportionally.

Theorem 6.5 Converse of the Triangle Proportionality Theorem
If a line divides two sides of a triangle proportionally, then it is parallel to the third side.

Source: McDougal Littel High School Geometry

## Triangle Midsegment Theorem

"How to prove and use properties of triangle midsegments. Yeah, it's that important."

## Corollary: Parallel Lines and Transversals

If three or more parallel lines intersect two transversals, then they cut off the transversals proportionally.

In the figure shown, if , then  and