Illustrative Mathematics
Similar Triangles
Proving triangles are similar is often an exercise in applying one of the many theorems young geometers memorize, like the AA similarity criteria. But proving that the criteria themselves are valid from basic principles is a great...
CK-12 Foundation
Ck 12: Dilation in the Coordinate Plane
[Free Registration/Login Required] Students will adjust Frankenstien's face to explore dilation. Click learn more to watch a video and click challenge me to answer a practice question.