Parallel Lines and Transversal

In this lesson we will learn about angle pairs in parallel lines. I cover corresponding, alternate interior, and same-side interior angles.

CORRECTION: I know, I know, I spelled "interirror" incorrectly in the video...twice. For the record it is "interior." I apologize, I'm a math guy and I am lost without spell check.

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transcript:

Welcome to Your Tutor Online video podcast. For today's lesson, we're going to look at parallel lines and angles that are formed when another line crosses them.

First, we need some definitions. Parallel lines are two lines which will never intersect or touch. They have the same slope. A transversal is a line that crosses two or more parallel lines. I numbered each of the angles formed by the transversal. We will use these numbers to refer to each angle. When we have parallel lines with a transversal, you can make conclusions about certain angle pairs. We will look at each of these pairs one at a time. The first angle pair is corresponding angles. It's easier if we look at each set of angles separately. Angles 1 through 4 is one set. And angles 5 through 8 is another.

Corresponding angles are in the same position in each group. Think of it in terms of which corner the angle is in. Angle 1 is in the top left corner of this set, so its corresponding angle is in the top left corner of the other set. So angle 1 and angle 5 are corresponding angles.

Corresponding angles are congruent. Meaning they have the same angle measure. For example, if you know that this angle is 37° and we know that its corresponding angle is also 37°. The angle we know about is in the top right corner, so the top right corner of the other group, (this one) is 37° also.

Next we'll look at alternate interior angles. There are two parts to this definition - alternate and interior. Let's look at interior part first. Interior means that the angle is in between the two parallel lines. In other words, inside this blue box I just drew, angles 3, 4, 5, and 6 are all interior angles.

Alternate means, to get to its pair, you need to cross the line and go to the other side. I'll start with angle 3. The alternate interior angle is 6. Because we crossed the line and go to the other side of the box. Alternate interior angles are also congruent.

For example, if you know this angle is 72°, then we know its alternate interior angle is also 72°. You crossed the line and go to the other side, so this angle is 72°.

The last angle pair we will look at in this lesson is same side interior angles. This is very similar to alternate interior angles, except they do not cross the line. The angles are still going to be in between two parallel lines, in other words, inside this blue box. Let's pick angle 4. The same side interior angle to angle 4 is angle 6 because it's the only angle you can get to without crossing any lines. Same side interior angles are supplementary which means they add up to 180°.

For example, if you know that this angle is 50°, then we can figure out the measure of its same side interior angle. This one is 130°, because 180 minus 50 is equal to 130. It's on the same side interior. That's the end of our lesson. If you need more help with this or other topics, visit www.yourtuturonline.com to find a tutor. yourtutoronline.com provides online tutoring services in a virtual classroom you just saw on this video. I'll see you next time. Thanks for watching. Class dismissed.