A straight angle measures 180° and looks as it is a straight line, therefore, it is a mathematical way of expressing a straight line. The two rays of the 180-degree angle are subtended towards the opposite direction, where the rays are joined to each other at endpoints.
Well, that's what we call a straight angle. It's just like a flat line that goes straight ahead. This angle is not only easy to visualize but also serves as a reference point for various geometric principles.
In this article, we will learn about Straight Angles by briefly learning about angles and their types.
What are Angles?
An angle is a geometric figure that represents the amount of rotation or deviation between two straight lines, rays, or line segments that meet at a common endpoint. The angle is denoted by the symbol “∠”.
What is a Straight Angle?
A straight angle is an angle that measures exactly 180 degrees (°). It is formed when two rays or lines point in exactly opposite directions, creating a straight line.
Straight Angle Definition
"Straight angle is defined as an angle that measures exactly 180°.
A straight angle is typically denoted as 180° or π radians (π rad)." When two rays meet and align in the same direction then the angle between them is 180° which is called a Straight Angle. We can understand from the name that since the rays are in a straight line hence it is called Straight Angle.
How many degrees in a Straight Angle?
A straight angle is an angle equal to 180°. It looks like a straight line. We know that an angle is formed when two rays meet. When two rays meet to form a Straight Angle which is equal to 180° then it can be seen that they are in one direction forming a Straight Line and hence called Straight Angle.
Properties of a Straight Angle
The different properties of Straight Angle are listed below:
- A straight angle always measures 180°.
- Straight angles create a straight line.
- It is denoted by π (i.e. π = 180°).
- It is also called the angle of a straight line.
- The two rays form a straight angle point in precisely opposite directions.
- It can be formed by joining two right angles (i.e. 90° + 90° = 180°)
Real-Life Examples of Straight Angle
We can find many objects around us forming a Straight Angle. Let's see some real-life examples of Straight Angle around us:
- 6 O'Clock: The minute hand on a clock points to the 12 at 12 o'clock and to the 6 at 6 o'clock, forming a straight line.
- Pencil: The body of a standard pencil is a straight line, extending from the eraser at the top to the tip at the bottom.
Straight Angles are applicable in real life in following:
- Architectural Precision
- Engineering Designs
- Art and Design Aesthetics
- Mathematics Education
- Optics and Physics
- Computer Graphics
Construction of Straight Angle
Construct a straight angle i.e., 180° angle, you can follow these steps using a protractor and a ruler:
Step 1: Using the ruler, draw a straight line (OA) horizontally across the paper.
Step 2: Take your protractor and align its center (the hole) with point O on your baseline.
Step 3: Extend the protractor's arm (the straight edge of the protractor) along line OA. Ensure
Mark a point at 180° on the protractor's scale. This point is directly opposite the center (point O) on the other side of the line OA.
Step 4: A to the point you marked at 180° on the protractor's scale. This line will form a straight angle with line AB.
Label the points where the two lines intersect, say, points A and B, to indicate that it's a straight angle.
Straight AngleFinally, a straight angle is constructed, which is a 180° angle.
Straight Angle in Pair
A straight angle pair, also known as a linear pair of angles, consists of two angles that combine to form a straight line. The sum of the measures of these two angles is always equal to 180°.
In other words, ∠AOC + ∠BOC = 180° i.e. ∠1 + ∠2 = 180°
Also Check:
Straight Angle Examples
Example 1: If you add a straight angle to a 60°, what will be the total angle measure?
Solution:
As we know, Straight Angle =180°
⇒ 60° + 180° = 240°
Example 2: There are two angles on a straight line if one of its angles is 75 °. Find another one.
Solution:
Let the angle be x ;
Given: another angle = 75°
Sum of all angles in the straight line is 180°
∴ x + 75 =180
∴ x = 180 - 75 = 105°
Example 3: Find the value of 'x' in the given figure below
Solution:
Given that,
Given: ∠AOC = 50° and ∠BOC = x
In the fig we can see that ∠AOB is straight angle i.e. 180°
∠AOB = ∠AOC + ∠BOC
⇒ 180° = 50 + x
⇒ x = 180° - 50°
⇒ x = 30°
Example 4: Find the value of ' x ' in given figure below, where O is the centre of circle.
Solution:
Given;
∠COD = 90° ( right angle )
∠BOD = 50°
∠AOC = x
In the fig we can see that ∠AOB = 180° ( angle of straight line )
∠AOC + ∠COD + ∠BOD = ∠AOB
putting values, we get
x + 90° + 50° = 180°
⇒ x = 180° - ( 90° + 50° )
⇒ x = 180° - 140°
⇒ x = 40°
Practice Questions on Straight Angle
1. Draw an Straight Angle and label its angle.
2. If you add a straight angle to a right angle, what will be the total angle measure?
3. Draw a simple picture of a straight angle. Label it and write down its degree measure.
4. Look around your room or outside your window. Can you find any objects or shapes that have straight angles? List a few examples.
5. Find the value of x.
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