Straight Angle, is essentially a perfectly straight line and measures 180°. Straight is the simplest and most basic angle in geometry.
Imagine a line that doesn’t bend or curve at all, just like a super straight road. 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. Let’s understand more about Straight Angles by briefly learning about angles and their types.
Table of Content
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 “∠”. Let’s learn what are the different types of angles.
Types of Angles
On the basis of measurement angles are classified as follows:
- Acute Angle: The angle which measures more than zero degree but less than 90° is called Acute Angle
- Right Angle: The angle which measures 90° is called Right Angle.
- Obtuse Angle: The angle which measures more than 90° but less than 180° is called the obtuse angle.
- Straight Angle: The angle which exactly measures 180° is called straight angle.
- Reflex Angle: The angle which measures more than 180 but less than 360° is called obtuse angle.
- Complete Angle: The angle which measures 360° is called Right Angle.
Apart from the above types of angles we also have angles which are in pairs. These are Complementary Angles and Supplementary Angles. Angles are also formed due to the intersection of two lines. On the basis of this, angles are classified as Vertically Opposite Angles, Corresponding Angles, Alternate Angles, and Consecutive Interior angles. Let’s move to the main motive of this article which is Straight Angle.
What is a Straight Angle?
Straight Angle is a perfectly straight line formed by two rays extending in opposite directions. It is an angle whose arms lie in opposite directions from the vertex and they join together to form 180°.
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.
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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 Angle
finally, 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°
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Solved Examples on Straight Angles
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 = xIn the fig we can see that ∠AOB = 180° ( angle of straight line )
∠AOC + ∠COD + ∠BOD = ∠AOB
putting values, we getx + 90° + 50° = 180°
⇒ x = 180° – ( 90° + 50° )
⇒ x = 180° – 140°
⇒ x = 40°
Practice Questions on Straight Angle
Q1. Draw an Straight Angle and label its angle.
Q2. If you add a straight angle to a right angle, what will be the total angle measure?
Q3. Draw a simple picture of a straight angle. Label it and write down its degree measure.
Q4. Look around your room or outside your window. Can you find any objects or shapes that have straight angles? List a few examples.
Q5. Find the value of x.
Straight Angles – FAQs
1. What is a Straight Angle in Geometry?
A straight angle is an angle that measures exactly 180°. It looks like a straight line, with no bending or turning.
2. How can we Recognize a Straight Angle visually?
A straight angle appears as a straight line with no curvature, formed by two rays extending in opposite directions from a common point.
3. How does a Straight Angle differ from a Right Angle?
A straight angle measures 180°, forming a straight line, while a right angle measures 90 °, creating an “L” shape.
4. How do we Measure a Straight Angle?
We can measure a straight angle using a protractor or any measuring tool that shows angles. Since it’s always 180°, you’ll see a half-circle on the protractor.
5. What is the Sum of the Angles in a Linear Pair?
The sum of the angles in a linear pair is always 180°. Linear pair forms a straight angle which is by definition, an angle that measures 180°.
6. How can I Draw a Straight Angle?
To draw a straight angle, simply draw a straight line. That line represents a straight angle.
7. Can you Make a Straight Angle with your arms?
Yes, if you stretch both of your arms out wide so that they are in a straight line, you are making a straight angle with your arms.
8. State some Real Life Examples of Straight Angles.
All the things, which looks straight are example of straight angle. Such as buildings, books, pencil, etc.
9. Can we Say that Angles in a Triangle make a Straight Angle?
No, a triangle cannot have an individual angle measure of 180°. In a triangle, the sum of its three interior angles always adds up to 180° i.e. (180 + x + x ≠ 180 ; x > 0).