 This video is called congruent or supplementary. What we're going to do is look at relationships between alternate interior angles, alternate exterior angles and on the next slide we'll look at the relationship between corresponding and consecutive interior. So quickly let's look at our graph and fill out our eight-angle forms. I know that vertical angles are congruent and that linear pairs are supplementary so if this is 125 both of these will be 55. Then down here same thing, 125 its vertical angle is congruent and then its linear pairs will be 55. So let's look for some relationships. Problem number nine says if two parallel lines are cut by a transversal then alternate interior angles are, well alternate interior remember we're looking for angle pairs that are on the opposite or alternate signs of the transversal and inside of these parallel lines. So I see 55 and 55 are on opposite sides of the transversal and inside the parallel lines and so are 125 and 125. So it looks like alternate interior angles are congruent. You can use the congruent symbol two equal signs with the squiggly. So when you have parallel lines alternate interior angles will be congruent. Now let's take a look at alternate exterior angles. So if two parallel lines, if two parallel lines are cut by a transversal then alternate exterior angles are, well remember alternate exterior are going to be on opposite sides of the transversal and outside of the parallel lines. So I have a pair of 55 and 55, 125 and 125. So it looks like alternate exterior angles are congruent. Alright, let's look at problem 11. Same picture, so let's quickly go through and mark our 125, 125 and the rest with 55 just like we had on the previous screen. So you should already have that part written on your note sheet. I just have to catch up to you. So now we're looking. Problem 11 says if two parallel lines are cut by a transversal then corresponding angles. Well remember corresponding, if you think of these lines as street lights, we've got an intersection or think of the lines as streets and the intersection as a stop light here and here corresponding they're in the same relative position according to the stop light. So at this intersection right here the 55 is in the upper left hand corner. Look at our other stop light or our other intersection. Its corresponding will also be in the upper left hand corner. So I see my upper lefts are both 55. My upper rights, my corresponding are both 125. My corresponding angles in the lower left are 125 and my corresponding angles in the lower right are 55. So it looks like corresponding angles are congruent. So far all of our angle relationships we've been looking at have been congruent. Let's see if we can get one that supplementary saving the best for last I guess. This one says if two parallel lines are cut by a transversal then consecutive interior angles are. Well consecutive interior for some reason are the hardest ones for students to remember but they're not bad. Consecutive interior are on the same side of the transversal and inside of your parallel lines. So I think these two the 125 and the 55 would be considered consecutive interior and my pair over here that are on the right side of the transversal would be another set. So I look it's obvious they're not congruent because this one is an acute angle it's bigger than 90 degrees and its consecutive interior match is acute. It's less than 90. So just by looking at them we know for sure we wouldn't call them congruent. They don't look the same. One is obtuse, one is acute. So then our other choice is to say that they are supplementary which seems to make sense. 125 plus 55 does add up to 180 so it does make sense for them to be supplementary. So just remember alternate exterior are congruent. Alternate interior are congruent. Corresponding are congruent and consecutive interior that's the only match that is supplementary.