There are many different types of angles and these can be classified based on the following characteristics.
First, let us see what an angle is and then we will show all the different types of angles .
In the figure above, the vertex is shown with a red dot and the arms are shown in blue.
We will define the basic angles. Here is a list of 7 types of angles based on the magnitude of the angle.
Study the images carefully so you understand them and then be able to recognize these basic angles quickly.
An angle whose measure is less than 90 degrees is an acute angle. For example, if the magnitude of an angle is 89 degrees, the angle is acute. The angle below is an acute angle.
An angle whose measure is exactly 90 degrees. The following is a right angle.
An angle whose measure is bigger than 90 degrees but less than 180 degrees is an obtuse angle. Thus, it is between 90 degrees and 180 degrees. For example, if the measure of an angle is 150 degrees, the angle is obtuse. The following is an obtuse angle.
An angle whose measure is exactly 180 degrees. Thus, a straight angle looks like a straight line. The following is a straight angle.
An angle whose measure is bigger than 180 degrees but less than 360 degrees. For example, if the measure of an angle is 235 degrees, the angle is a reflex angle. The following is a reflex angle.
Full rotation angle:
An angle whose measure is exactly 360 degrees is a full rotation angle. A full rotation angle consists of 4 right angles. The following is a full rotation angle.
An angle whose measure is exactly 0 degree is a zero angle. A zero degree angle has both arms on the same line. The following is a zero degree angle.
Two types of angles are formed when the angle is either measured in counterclockwise direction, or a clockwise direction.
If we measure an angle counterclockwise or in the opposite direction the hands of a clock move, the angle is a positive angle. The angle below is a positive angle.
If we measure an angle clockwise or in the same direction the hands of a clock move, the angle is a negative angle. The angle below is a negative angle.
Here is a list of 4 types of angles based on a pair of angles.
Angles with a common vertex and one common side are called adjacent angles.
<a and <b are adjacent angles and the common side is red.
Two angles whose measures add to 90 degrees are complementary angles. Angle x and angle y shown below are complementary angles because together they form a right angle.
For example, suppose angle x is equal to 30 degrees and angle y is equal to 60 degrees. Since 30 degrees + 60 degrees = 90 degrees, angle x is the complement of angle y (another way to say they are complementary).
Two angles whose measures add to 180 degrees are supplementary angles. Angle c and angle d shown below are supplementary angles because together they form a straight angle.
For example, suppose angle c is equal to 70 degrees and angle d is equal to 110 degrees. Since 70 degrees + 110 degrees = 180 degrees, angle c is the supplement of angle d (another way to say they are supplementary).
Angles that have a common vertex and whose sides are formed by the same lines are called vertical angles or opposite angles. Angle α (alpha) and angle θ (theta) are vertical angles.
When two parallel lines are crossed by a third line (Transversal), 8 angles are formed. Take a look at the following figure.
Angles 3,4,5,8 are interior angles
Angles 1,2,6,7 are exterior angles
Alternate interior angles:
Alternate interior angles are pairs of interior angles on opposite sides of the transversal.
For instance, angle 3 and angle 5 are alternate interior angles. Angle 4 and angle 8 are also alternate interior angles.
Alternate exterior angles:
Alternate exterior angles are pairs of exterior angles on opposite sides of the transversal.
Angle 2 and angle 7 are alternate exterior angles.
Pairs of angles that are in similar positions are corresponding angles
Angle 3 and angle 2 are corresponding angles.
Angle 5 and angle 7 are corresponding angles
Here we go! Study the types of angles carefully. This is where any serious study of geometry begin.