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Three Theorems Involving Proportions - Lesson 8-5

Today, learned some theorems that prove useful when solving problems involving similar triangles. We started with the side-splitter theorem:

For those of you who are interested, here's the proof for the side-splitter theorem:

Next, we applied the side-splitter theorem to parallel lines:

Finally, we looked at the proportions we can set up if we have an angle bisector...this is a nice proof, huh?

We ended by solving the following problem...the first proportion is straight forward, but don't get fooled (again...) by the second one! Make sure you understand why it is set up the way it is!