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Lesson 74: More About Angles
You've learned the basics of angles in a previous lesson. This lesson teaches you a bit more about them, and introduces you to some definitions that you need to know.
Take a look at the angles below. An angle is formed when two lines meet at a point. The point at which they meet is called the vertex of the angle. Each line is called a ray. It has an arrow on one end, meaning it goes on forever, and a point on the other end.
You've seen the first angle before in a previous lesson. It's a right angle, which is said to have a measurement of 90°. It's formed by two straight lines, one going straight up and down, and one going straight left and right. Of course the whole angle could be rotated, and it would still be a right angle, but drawing it this way makes it easy to see.
Next is an acute angle which has a measurement of less than 90°. The picture shows an example.
Next as an obtuse angle which is bigger than a right angle, but smaller than a straight angle which you'll see next. It has a degree measurement between 90° and 180°.
Next is a straight angle. Starting at the vertex, it has rays that extend outward in opposite directions. It just forms a straight line. It has a degree measurement of 180°.
Later you'll learn much more about angles, but this just introduces you to some more definitions which you should memorize.
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