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CK-12 Foundation
Ck 12: Geometry: Polygon Similarity Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide looks at similar polygons, scale factor (ratio), and triangle similarity.
Homeschool Math
Homeschool Math: Introduction to Sine
This is an introductory lesson about the trigonometric function sine. Students will study several similar right triangles and the ratio of certain two sides in them.