The test can either draw that little square, the perpendicular sign, which is that little square, or it can indicate that the angle is 90 degrees. If the two lines or segments meet at right angles, they are called perpendicular, that is a term you should know. There are actually four right angles at that intersection. So here we have two lines intersecting at right angles. That's 180 degrees, there are 90 degrees in a right angle. But if there's any point on the straight line, all the way around from one side of the line to the other. In a straight angle, there are 180 degrees and of course remember a straight line can go in any direction. We'll do a quick review of basic degree facts. They could give us other information and say find x. This flexible format allows them either to specify the angle, for in the text, they could say x = 50, or they could ask a question about it. Actually, the probably it's favorite thing to do is the following just specify angle, with a variable number degrees.
![magoosh math flash cards magoosh math flash cards](https://www.educationalappstore.com/images/screenshots/app10665/3.jpeg)
We can just use that to talk about that measure, in the number of degrees in the text. So angle GFH = 50 degrees because they put letters on the points in the diagram.
![magoosh math flash cards magoosh math flash cards](https://image.slidesharecdn.com/gre-flash-cards-181205183829/95/gre-flash-cards-3-638.jpg)
Alternately, the test can label the diagram and state the measure of the angle in the text. The test can state these directly, so 50 degrees.
![magoosh math flash cards magoosh math flash cards](https://apprecs.org/ios/images/app-icons/256/cc/412496588.jpg)
We measure the size of an angle in degrees. Although the test is often careful enough, to use a three-letter name always for an angle. Theoretically, that could occur on the test. For example, there's only one angle in this diagram. Sometimes in these videos I'll also use the single angle name, if there's no ambiguity. And so, we can call either CDE or EDC, as long as the vertex is in the middle. Right here, the point of the angle must be in the middle of the name. We could call this angle either CDE or EDC, Point D, the vertex of the angle. If we label points, we can talk about an angle. That is what an angle is, it's that dynamic space in between the two lines. So in other words, going from here to here. The best way to understand an angle is to think of it dynamically, as the act of turning or rotating. This happens to be between one line and one segment. An angle occurs between two lines, or two segments. Or it can mean the length of the line segment, the numerical length. And for the purpose of the test, AB can either mean the actual shape of the line segment itself. And when these endpoints are labeled, that makes it easy to discuss. So for example, here we have a line segment, it has two endpoints. A line segment is a finite piece of a line. People mistakenly assume that this also means they can assume lines are horizontal, and that is not correct. Then when we say that you can assume from the test, that lines are straight. Now people get really confused on this, if you are confused, if you think that horizontal and straight mean the same thing. But some lines are drawn horizontally for convenience, but you can never assume that lines are exactly horizontal or vertical, simply because they appear so. And you can always assume that a line is straight on the test. So all the lines that we had on the previous slide, lines going in different directions, all of those are straight lines. Those two words have very different meanings, but sometimes, there are some students who confuse them. It's very important not to confuse straight with horizontal. So here we have a bunch of different straight lines, in a bunch of different directions.You have to imagine that at the end of each line there are some arrows or something like that, to indicate that the lines actually do go on forever in both directions. Lines are straight and they go on forever in both directions. You're using your hands, you're engaging every part of the brain and will make it much easier, to understand all these relationships. Use your hands, our hands are actually part of our intelligence. Actually build triangles, build rectangles, actually look at them. You can use pencils, toothpicks, straws, anything like that. After you watch these, get out paper and a ruler and draw these different shapes, actually physically draw them on paper. It is not enough simply to watch these videos. Especially for the folks who are, for whom Geometry is a little bit harder, here's what I'm gonna say.
![magoosh math flash cards magoosh math flash cards](https://s.cafebazaar.ir/1/upload/screenshot/com.magoosh.flashcards.gmat.idioms-screenshots-6.png)
And other people who have not developed their visual skills, Geometry can be a little bit harder. Now for some people who are visually oriented, Geometry comes very naturally. And Geometry of course, is the study of shapes.