Lesson 12
Practice With Proportional Relationships
Lesson Narrative
This optional lesson gives students an additional opportunity to practice finding unknown values in proportional relationships using contextual examples. The problems preview using the Pythagorean Theorem, which is a key idea in a subsequent lesson. They also preview finding all unknown values in right triangles, which is a key idea in a subsequent unit. Students have a chance to reason abstractly and quantitatively as they think about whether their answers make sense in context (MP2).
Learning Goals
Teacher Facing
 Calculate unknown values in proportional relationships.
 Determine scale factors to describe similar figures (using words and other representations).
Student Facing
 Let’s find unknown values in proportional relationships.
Required Materials
Learning Targets
Student Facing
 I can find scale factors and use them to solve problems.
CCSS Standards
Addressing
Glossary Entries

similar
One figure is similar to another if there is a sequence of rigid motions and dilations that takes the first figure onto the second.
Triangle \(A'B'C'\) is similar to triangle \(ABC\) because a rotation with center \(B\) followed by a dilation with center \(P\) takes \(ABC\) to \(A'B'C'\).