This video first introduces the AA Triangle Similarity Postulate and the SSS & SAS Similarity Theorems. Then it gets into the triangle proportionality theorem, which also says that parallel lines cut transversals proportionately they cut triangles.
Using SSS & SAS Similarity Theorems
This video goes through a bunch of the most common similar triangles problems you'll see, including the ones where you have to say if two triangles are similar or not and why. It also shows a couple of common diagrams for proportional triangles that you should know.
Similar Triangle Proofs
In this video I do a few proofs using the AA Postulate, and the SAS Similarity Theorem. And I explain what to look for in these types of proofs, where the given info sometimes includes random equations like AB x BD = CB x AD.
Right Triangle Similarity Theorems: "Geometric Mean"
There are three theorems about right triangles which have been cut in half with the "altitude to the hypotenuse". These geometric mean theorems are super-confusing, so I explain how to make sense of it by always setting up a proportion so you don't have to memorize the crazy equations.
Parallel Lines & Proportional Transversals
This video covers the problems where you have three parallel lines that are cut by more than one transversal, and the theorem that says the transversals will be cut into proportional segments by the parallel lines.
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)