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Texas Education Agency
Texas Gateway: Generalizing Proportions From Similar Figures
Given a pair of similar figures, including dilations, students will be able to generalize that the lengths of corresponding sides are proportional.
CK-12 Foundation
Ck 12: Geometry: Ratios and Proportions Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide reviews ratios, proportions, and cross-multiplication.