Straight Angle

Angle that measure exactly 180 degree is a Straight Angle.

Remember the keyword here is exact 180 degree
If the angle is less than 180 degree, it is known as Obtuse Angle
And if the angle is greater than 180 degree, it is known as Reflex Angle

Some examples of Straight angle are given below:

What is straight angle

From the above examples, you can observe two properties of 180 degree angle:
(a) 180 degree angle form a complete straight line

(b) With straight line angle, the direction gets completely opposite.
For example, if you are looking towards north, a 180 degree movement will change your direction towards south.

Straight angle definition in Geometry

(c) Straight Angle is half of revolution

Full revolution is 360 degree

Straight Angle and Its Part

Straight angle is made of two line, joined at a common point exactly at 180 degree angle.

Some important parts of Right Angle are:

(a) Arms
The two lines forming the angles are known as Arms

Here OA and OB are the two arms of the straight angle

What is arm in angle

(b) Vertex
The common point where two lines join is called Vertex

Here the Point O is the vertex

What is Vertex in angle

Drawing Straight Angle using Protractor

In Fact you don’t need a protractor to draw 180 degree on paper.
Just draw a horizontal line on paper.
Mark point O at the center and point A & B on opposite ends.

How to draw straight angle using protractor

See it is so easy to draw 180 degree angle.
You don’t need any help of Protractor for making 180 degree, but still if you want to understand the angle making using protractor, read the below instructions.

Making 180 degree angle using Protractor

(a) Take sheet of paper and draw horizontal line OA

Construct straight angle using protractor

(b) Place center of Protractor at point O

Learn about straight angle for Grade 5

(c) Base OA is on right side of Protractor.
So start counting angle from right side and mark point B at number 180

Draw straight angle in geometry

(d) Join points OB and you will get 180 degree angle AOB

What is straight angle in geometry

Straight Angle – Practical Example

(a) Ruler

Straight angles examples in real life

(b) Ladder

Ladder forms straight angle

(c) Railway Track

Railway track form straigh angle

FAQ’s on Straight Angle

(01) What is the angle measurement of straight angle?

Read Solution

Exactly 180 degree

(02) Can 181 degree angle measurement called straight angle?

Read Solution

No, the measurement should be exact 180 degree

(03) How to draw straight angle?

Read Solution

The process is very easy.
Just draw a straight line with the help of ruler and you will get straight angle

(04) What is half of straight angle?

Read Solution

We know that:
Straight\ Angle\ =\ 180\ degree\\\ \\ \frac{Straight\ Angle}{2} \ =\frac{180}{2} \ =\ 90\ degree\\\ \\

Hence, half of straight angle is right angle

(05) Can we make straight angle using right angle?

Read Solution

We know that straight angle = 180 degree
And, Right angle = 90 degree

So, if we add two right angle, we will get a straight angle
⟹ 90 + 90 = 180 degree

draw straight angle adding right angle

(06) Is Reflex angle same as straight angle?

Read Solution

No !!
Straight angle is exactly 180 degree
While reflex angles starts from angle greater than 180 degree

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