Angles ABD and Angles are CBD are adjacent angles

∠A or ∠ABC

A

.

.

.

C

B

An angle is formed when two lines (rays) meet at a common point called a vertex. A ray is a line with a start point but doesn’t have an endpoint. Angles can be named by this vertex. The angle symbol ∠ is used to write an angle mathematically. A common method for naming angles is by using three points. Two points for the rays and one for the vertex.

In Geometry angles are classified according to their angle measure. The main angle classifications are: acute angle, obtuse angle, right angle, reflex, and straight angle.

90°

110°

30°

60°

Complementary Angles are two angles that their angle measure add to 90 degrees.

110°

Congruent Angles are two angles that have equal angle measure.

90°

Supplementary Angles are two angles that add to 180 degrees.

A Reflex Angles measures greater than 180 degrees

Transcript

Hi, welcome to Moomoomath. Today we are going to look at **classifying angles**.The first angle we are going to look at is a *90 degree angles* that makes an L shape and the symbol is a square box in the corner. Then we have a *straight angle* which is straight across without an actual angle. It thinks of it as a straight line. Then you have an angle that measures smaller than 90 degrees and that is an *acute angle*. Then you have an **angle** that is larger than 90 but less than straight and that is an obtuse acute. So, let’s label those. This first one is 90 and that is your *reference angle*. You always want to be familiar with your **90 degree angle **to see if you have one that is smaller. So that one is an acute angle. This one is larger than 90 degree and you can sketch in your L, if you want to, to compare it. That one is greater so it is obtuse. And a straight line is 180 degrees. It is two, **90 degree angles** put together. So this is your straight angle. So you are always comparing to your 90 degree angle or your right angle. So that is how angle are classified. So let’s look at the rules of angles. OK, an acute angle is an angle that is less than 90 degrees. A right angle is equal to 90 degrees. Your right angle is your reference angle. Then you have an obtuse angle that is greater than 90 and a straight angle which is equal to 180 degrees. You can use a protractor to measure those. And when you measure the angle with a protractor you are going to take the dot on the protractor and line it up with the *vertex*. What is the *vertex*? It is the corner of the angle. You are going to line it up and read it from the bottom up from 0. There is another video on protractors and how to use those. This is how you **classify angles**. Hope this is helpful!

Acute Angles measure from 0 to less than 90 degrees

Angles are measured from the vertex which is the point of intersection of the two lines.( Labeled A in this example)

A Straight Line measures exactly 180 degrees

An Obtuse angle measures greater than 90 degrees and less than 180 degrees

A Right Angle measures exactly 90 degrees. The square at the vertex tells you it is a right angle.

A

A