180 Degree Angle – Definition, Construction, Facts, Examples, FAQs

What Is a 180 Degree Angle?

The 180 degree angle is an angle that forms a straight line. The 180 degree angle in radians is or about 3.14 radians.

You can see that the straight line is formed when the two arms of the angle (BA and BC) are opposite rays. The two arms extend in the opposite directions. Thus, the 180 degree angle is also called ‘a straight angle.’

How to Draw a 180 Degree Angle

There are two methods to draw an accurate 180 degree angle: using a compass or using the protractor.

Constructing 180 Degree Angle Using Protractor

Step 1: Draw ray OA. Align the center of the protractor with the point O. O will be the vertex of the angle.

Step 2: Mark the 180 degree reading (on inner calibration) as point B.

Step 3: Join OB.

∠AOB = 180^o

Constructing 180 Degree Angle Using Compass

Here are the steps to assist you in drawing 180 degree angle using a compass: 

Step 1: Draw a straight line and name it PQ.

Step 2: Mark a point between PQ using a dot and name it as O.

Step 3: Place the compass on the point O and make an arc that starts on OQ and ends on OP, making a semicircle.

Step 4: Name the points of intersection of the arc with OP and OQ as X and Y respectively. 

∠YOX = 180^o

Negative 180 Degree Angle

The straight angle if measured clockwise is a negative straight angle (-180^o).

180 Degree Angle Name

As we mentioned earlier, the 180 degree angle forms a straight line. So, it is also known as a “Straight angle” or“flat angle.”

Types of angles formed by a 180 degree angles:

• Half of 180^o angle measures 90^o. It is known as a right angle.
• Twice the 180^o angle measures 360^o. It is known as a complete angle or a full angle.
• Angles greater than 180^o and less than 360^o are called reflex angles.
• Angles between 90^o and 180^o are called obtuse angles.

Facts about 180 Degree Angle

Conclusion

In this article, we learned about the 180 degree angle (straight angle), and its construction using protractor and compass. Let’s solve a few examples and practice problems based on the concept of 180 degree angle.

Solved Examples on 180 Degree Angle

Example 1: What is the measure of the angle BOC?

Solution: 

The straight angle is 180 degrees. Thus, two angles making a straight angle will add up to 180 degrees.

Here, ∠AOB =  40^o

Let us assume that  ∠BOC = x. 

x + 40^o = 180^o

x = 180^o – 40^o

x = 140^o

Example 2: How is 180 degree angle related to a complete angle and a right angle? 

Solution: 

A complete angle measures 360 degrees. 

Half of the complete circle angle is 180 degree angle.

 Right angle measures 90 degrees.

Twice the right angle is a straight angle. Two adjacent right angles form a straight angle.

Example 3: What is the angle made by the hour hand and the minute hand when the clock reads 06:00?

Solution: 

Practice Problems on 180 Degree Angle

Frequently Asked Questions about 180 Degree Angle