Points, Lines & Angles in Geometry

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• 0:02 Points
• 1:17 Lines
• 2:31 Angles
• 3:30 Right Angles
• 3:50 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

After watching this video lesson, you should understand the basic terms that form the foundation of geometry. Learn what a point is, what a line is, what an angle is, and learn about a special type of angle called a right angle.

Points

You and your friend are looking at a map on your friend's smart phone. You see a blinking blue dot showing you where you are, and you see another red dot showing you where the burger joint is that you two want to get to. These dots are called points in geometry. As it happens, points are one of the most basic things you can understand in geometry. Without points, geometry would be dead! Yes, it is that basic!

As you can see, points are very useful, even in the real world. Without them, you wouldn't know where you are on a digital map! Even though the points on the map aren't labeled, we can label them if we want to. We can label them with a capital letter, such as Y or B, or we can label them with what they stand for, such as 'you are here' or 'burger joint.'

We can even draw a grid with a horizontal x-axis and a vertical y-axis. We mark our numbers on our axes so that the point where they cross is (0, 0). Then we can tell people the location of our point on this grid system:

If our point is located three spaces above the x-axis and four spaces to the right of the y-axis, then we say that our point is located at (4, 3). So, there we have our basic point.

Lines

Now, imagine that you are picking people who want to be on your volleyball team. You take a stick and draw a straight bar in the sand and you tell people that whoever wants to be on your team needs to be on the same side as you. You have just drawn a line, which is another basic item in geometry. A true line in geometry is a straight bar that keeps going and going in both directions. We label lines by labeling any two points on the line and call the line by those two points. So, a line that has the two points D and E in it is called line DE.

If a line has a beginning and an end, then we call it a line segment. Any lines that we draw, such as the one you drew in the sand, are line segments. We label line segments by their beginning and end point. So, line segment AB has a beginning point of A and an end point of B.

If the line has a beginning but no end, then we call it a ray. We label rays by their beginning point and another point on the ray. So, ray FE has a beginning point of F and another point E on the ray.

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