CK-12 Geometry Concepts

http://www.ck12.org Chapter 7. Similarity

Example C

IsDE||CB?

Use the Triangle Proportionality Converse. If the ratios are equal, then the lines are parallel.
6
18 =

1

3 and

8

24 =

1
3
Because the ratios are equal,DE||CB.

Watch this video for help with the Examples above.

MEDIA

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CK-12 Foundation: Chapter7TriangleProportionalityB

Vocabulary

A line segment that connects two midpoints of the sides of a triangle is called amidsegment. A midpoint is a point
that divides a segment into two equal pieces. Pairs of numbers areproportionalif they are in the same ratio.

Guided Practice

Use the diagram to answers questions 1-5.DB‖F E.

1. Name the similar triangles. Write the similarity statement.

2.BEEC=FC?

3.ECCB=CF?

4.DB? =BCEC

5.FCFC+?=F E?

Answers:

1. 4 DBC∼4F EC


2. DF


3. DC


4. FE


5. DF; DB

Practice

Use the diagram to answer questions 1-5.AB||DE.

1. FindBD.


2. FindDC.


3. FindDE.