CK-12 Geometry-Concepts

7.8. Triangle Proportionality http://www.ck12.org

7.8 Triangle Proportionality

Here you’ll learn how to apply both the Triangle Proportionality Theorem, which states that if a line that is parallel
to one side of a triangle intersects the other two sides, then it divides those sides proportionally.

What if you were given a triangle with a line segment drawn through it from one side to the other? How could you
use information about the triangle’s side lengths to determine if that line segment is parallel to the third side? After
completing this Concept, you’ll be able to answer questions like this one.

Watch This

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URL: http://www.ck12.org/flx/render/embeddedobject/52550

CK-12 Foundation: Chapter7TriangleProportionalityA

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URL: http://www.ck12.org/flx/render/embeddedobject/1354

James Sousa: Triangle Proportionality Theorem

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URL: http://www.ck12.org/flx/render/embeddedobject/1355

James Sousa: Using the Triangle Proportionality Theorem to Solve for Unknown Values

Guidance

Think about a midsegment of a triangle. A midsegment is parallel to one side of a triangle and divides the other two
sides into congruent halves. The midsegment divides those two sidesproportionally.