This is an applet that will help you investigate why SAS Similarity is valid.

[b]Given construction: ∠B≅∠D and the sides that include this angle are proportional.[/b][br][br]Explore: Move points A, B, or C.[br]How does this affect the remaining angles and ratio of the 3rd side?[br]Using the given construction, are these two triangles similar?[br][br]Explore: Change the scale factor.[br]How does this affect the remaining angles and ratio of the 3rd side?[br]Using the given construction, are these two triangles similar?