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Basic Facts about Parallel Planes - Lesson 6-3

Today, we started with the following warmup problem:

After reviewing the 6.2 homework, we discussed some basic facts about parallel planes. We started by defining what it meant for lines and planes to be parallel, for planes to be parallel and for lines to be skew.

We then discussed the following theorem. This is a key theorem to understand!!

The proof for this should make sense...I won't ask you to prove it, but you should understand it. Basically, since m and n are parallel planes, they never intersect. That means that line AB and line CD never intersect. Since those lines are on the same plane (and never intersect), they have to be parallel by definition.

With this information, we talked about the following properties of lines and planes. Make sure you know these...they are great fodder for sometimes, always, never type questions!!

Before going over homework, we went through the following example. Note the use of some of the theorems we've covered!!