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9. Similarity
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United States of America
Grades 9-12

9.03 Proving triangles similar

Lesson
Practice
Adaptive
Worksheet

Interactive practice questions

Consider the triangles below.

a

Which of these triangles are similar?

A

B

C

D
b

Give a suitable reason for their similarity.

All sides are in the same ratio.

A

All corresponding sides are congruent.

B

All corresponding angles are congruent.

C
Easy
< 1min

The pair of triangles in the diagram already have one pair of angles identified as being equal.

Easy
< 1min

Consider the diagram below.

Easy
< 1min

Consider the diagram below.

Easy
< 1min
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Outcomes

G.SRT.A.2

Given two figures, use the definition of similarity in terms of similarity transformations to decide if they are similar; explain using similarity transformations the meaning of similarity for triangles as the equality of all corresponding pairs of angles and the proportionality of all corresponding pairs of sides.

G.SRT.A.3

Use the properties of similarity transformations to establish the aa criterion for two triangles to be similar.

G.SRT.B.4

Prove theorems about triangles. Theorems include: a line parallel to one side of a triangle divides the other two proportionally, and conversely; the Pythagorean theorem proved using triangle similarity.

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