In geometry, we come across various shapes and sizes. These shapes are defined in two-dimensional and three-dimensional space. The two-dimensional shapes or 2d shapes are circles, triangles, squares, pentagons, hexagons, etc. The three-dimensional shapes or 3d shapes are cubes, cuboids, spheres, cones, etc. The shapes are basically categorized based on their sides and the types of angles included between them.

The fundamental of shapes begins with angles, lines and points. Point is essentially a dot where two lines are consolidated. A line is a straight one-dimensional figure, that extends indefinitely in both directions and has no thickness. An angle is shaped when two lines are associated with one another, end to end. These angles are measured in degrees or radians. Let us read this article to learn more about the angles.

Classification of Angles

Angles are formed when two rays are joined end to end at a point and the arms of the angle extend indefinitely. Based on the measurements, the angles are classified into six different types, they are:

  • Acute angles
  • Obtuse angles
  • Right angle
  • Straight angle
  • Reflex angle
  • Full rotation

Let us learn more about these angles.

Acute Angle

The angle that measures less than 90 degrees is called the acute angle. The examples of acute angles are 30°, 45°, 60°, 89°, etc.

Acute angle < 90°

Obtuse Angle

The angle that measures more than 90 degrees is called the obtuse angle. The examples of obtuse angles are 91°, 130°, 145°, 160°, 179°, etc.

Obtuse angle > 90°

Right Angle

The angle that is exactly equal to the 90 degree angle, is called the right angle. The arms of the angle are perpendicular to each other.

Right angle = 90°

Straight Angle

We have learned till now, angle greater than 90 degrees, less than 90 degrees and equal to 90 degrees. But a straight angle is not defined based on 90 degrees.

A straight angle is an angle that is exactly equal to 180 degrees. This is named as straight because it appears as a straight line. Another important point is, when we add two right angles, we get a straight angle. It is also called 180 degree angle.

Straight angle = 180°

Reflex Angle

The angle which is greater than 180 degrees is called reflex angle. In other words, it is also called complementary angle to the acute angle.

Reflex angle > 180°

Full Rotation or Full Angle

The angle that is exactly equal to 360° is called full rotation or full angle. The sum of two straight angles will result in a full angle.

180° + 180° = 360°

Full Rotation = 360°


The angles which we have discussed above are the basic types of angles. Some angles are defined based on direction such as positive and negative angles. The positive angles are measured in anticlockwise direction whereas the negative angles are measured in clockwise direction.

Also, there are pairs of angles that are described when the angles are paired at the same time. Some of such angles are:

  • Supplementary Angles (Sum of two angles is 180 degrees)
  • Complementary angles (Sum of two angles is 90 degrees)

Hence, in geometry we have come across variety of angles which are easy to learn and remember.


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