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Warm Up
Similarity in Triangles
Unit 13 Notes
Definition of Similarity
What does it mean to be Similar?
Similarity Definition• Two polygons are similar polygons if corresponding
angles are congruent and corresponding side lengths are proportional.
This is called the Similarity Ratio.
Ex.1 Use similarity statements.
Vocabulary: Similarity RatioIf two polygons are similar, then the ratio of the
lengths of two corresponding sides is called the Similarity Ratio.
In Example 1 the common ratio of is the similarity ratio of to ΔXYZ.
Is the similarity ratio the same From ΔXYZ to ΔRST?
You Try!
Given ΔJKL ~ ΔPQR, list all pairs of congruent angles. Write the ratios of the corresponding side lengths in a statement of proportionality.
Standardized Test Practice
Ex.2 Are the 2 triangles similar? If so, write a similarity statement. What is the similarity ratio from ΔCDE to ΔVUT?
YesΔCDE~ΔTUV
You Try!In the diagram, ΔABC ~ ΔDEF. Check that
the ratios of corresponding side lengths are equal. What is the scale factor from ΔABC to
ΔDEF? 𝟓𝟕
Standardized Test Practice
Scale Factor for Dilation
Is NOT the same as a
Similarity ratio
Congruent FiguresCongruent figures are also considered to be
similar figures. What would be the similarity ratio between any two congruent
figures?
1:1
Ex.3 Use Similar Polygons
I
Are there other Ways to set up a
Proportion in this problem?
In the diagram, ΔXYZ ~ ΔPQR. Solve for the missing side.
You Try!
25
HW Assignment
• Blue Workbook–Section 6.1 #19-24–Section 6.3 #1-4, 16-19
Proving Triangles Similar
Unit 13
SHORTCUTS
Angle-Angle (AA) Similarity Postulate
Examples of AA
Side-Side-Side (SSS) Similarity Postulate
Examples of SSS
Side-Angle-Side (SAS) Similarity Postulate
Examples of SAS
Are the triangles similar? Why or Why Not?
A few more…
Are these triangles similar? Why or Why not?
HW Assignment
Warm Up- Take Notes Over Videohttp://youtu.be/tm-_6sFdfk8
Practice
Partner Project
Proving Pythagorean Theorem
Using Similar Triangles
Unit 13
45.G.SRT.4
Proving the Pythagorean Theorem using Similar
Triangleshttp://www.khanacademy.org/math/geometry/triangles/v/pythagorean-theorem-proof-using-similarity
Assignment
Handout(Proving the Pythagorean Thm and Shadows)
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