Geometry is fun if the concepts of lines, curves, planes, angles etc are clear to you. If you understand what is a line and a surface in geometry, then the next thing that you need to understand is an angle. We use angle everywhere in our daily lives. While watching any sports such as cricket, soccer, table-tennis etc; we have to use the term angle to refer to the direction of the ball. Angles in geometry are similar to the angles that we understand in real life but they are better defined in geometry. Before we try to understand the type of angles in geometry, it would be better to recall the definition of an angle in geometry.
An angle refers to the figure which is formed by two rays originating from a common end point. The end point is referred as the vertex of the angle, while the two rays are termed as the arms or sides of the angle. An angle may also be formed by the intersection of two surfaces. For example, when you open your book, an angle is formed between two pages where each page is representing a plane.
Let us try to understand the different types of angles in geometry
Angles are measured in terms of angles or radians. There are total 360 degrees or 2π radians in one complete rotation of a circle. Thus, if the two arms of an angle cover one-quarter of a circle, the angle measure one-fourth of the angles in a complete circle, i.e. 90 degrees or π/2 radians. The degree is more commonly used as the unit for measurement of angles. Let us now try to understand the various types of angles in geometry.
Following are the different types of angles in geometry:
1. Acute Angle: If the angular separation between the arms of an angle is between 0 degrees and 90 degrees, it is called as an acute angle.
2. Right Angle: If the angular separation between the two arms of an angle is exactly 90 degrees, then it is called as a right angle.
3. Obtuse Angle: If the angular separation between the two arms of angle is more than 90 degrees but less than 180 degrees, then it is called as an obtuse angle.
4. Straight Angle: If the angular separation between the two arms of an angle is exactly 180 degrees, then it is called as a straight angle. A straight angle looks like a straight line with a dot in the centre.
5. Reflex Angle: If the angular separation between the arms of an angle is more than 180 degrees but less than 360 degrees, then it is called as a reflex angle.
Note: All the angles measured in the anti-clockwise direction. If the angles are measured in the clockwise direction, they are termed as negative angles.
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