Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store

What's the Difference Between an Obtuse and an Acute Angle?

ffImage
banner
widget title icon
Latest Updates

widget icon
Start Your JEE Practice Here :
JEE Test Series 2026

How Can You Identify Obtuse and Acute Angles Easily?

To differentiate between obtuse and acute angles: Angles play a fundamental role in understanding the relationships between lines, shapes, and objects. Two important classifications of angles are obtuse and acute angles. An obtuse angle is any angle that measures greater than 90 degrees but less than 180 degrees. It appears wider and more open than at a right angle (90 degrees). On the other hand, an acute angle is any angle that measures less than 90 degrees. It appears narrower and more compact compared to a right angle. Obtuse and acute angles can be found in various geometric configurations, such as triangles, quadrilaterals, and polygons, and their measurements and properties provide insights into the characteristics and properties of these shapes. Let’s understand them further in detail.


Category:

JEE Main Difference Between

Content-Type:

Text, Images, Videos and PDF

Exam:

JEE Main

Topic Name:

Difference Between Obtuse and Acute Angle

Academic Session:

2026

Medium:

English Medium

Subject:

Mathematics

Available Material:

Chapter-wise Difference Between Topics


Defining Obtuse Angle?

An obtuse angle is a type of angle in geometry that measures greater than 90 degrees but less than 180 degrees. It appears wider and more open than a right angle (90 degrees) but falls short of forming a straight line (180 degrees). In an obtuse angle, one of the rays extends beyond the perpendicular position, creating an angle that is larger than a right angle. The vertex of an obtuse angle is always located between the two rays. Obtuse angles are commonly encountered in various geometric shapes and can provide valuable insights into the relationships and properties of angles, lines, and polygons. The features of obtuse angles are: 


  • Measurement: An obtuse angle measures greater than 90 degrees but less than 180 degrees.

  • Ray Extension: One of the rays of an obtuse angle extends beyond the perpendicular position, forming an angle that is larger than a right angle.

  • Vertex Position: The vertex of an obtuse angle is always located between the two rays.

  • Shape: An obtuse angle appears wider and more open compared to a right angle (90 degrees) but falls short of forming a straight line (180 degrees).

  • Relationship to Right Angle: An obtuse angle is larger than a right angle but smaller than a straight angle.

  • Naming: In geometric notation, an obtuse angle is often denoted using three points, with the vertex as the middle point, such as ∠ABC.

  • Angle Relationships: Obtuse angles can interact with other angles, forming complementary angles (when combined with another angle to form a right angle) or supplementary angles (when combined with another angle to form a straight angle).


Defining Acute Angle?

An acute angle is a type of angle in mathematics that measures less than 90 degrees. It appears narrower and more compact compared to a right angle (90 degrees). In an acute angle, both rays originate from the same endpoint and form a sharp V-shape. The vertex of an acute angle is located between the two rays. Acute angles are commonly found in geometric shapes, such as triangles, where all interior angles are acute. Understanding acute angles is essential for analyzing the properties and relationships of angles, lines, and polygons in geometry. The features of acute angles are:


  • Measurement: An acute angle measures less than 90 degrees.

  • Ray Configuration: The two rays of an acute angle originate from the same endpoint, forming a sharp V-shape.

  • Vertex Position: The vertex of an acute angle is located between the two rays.

  • Shape: An acute angle appears narrower and more compact compared to a right angle (90 degrees).

  • Relationship to Right Angle: An acute angle is smaller than a right angle but larger than a zero angle (a straight line).

  • Naming: In geometric notation, an acute angle is often denoted using three points, with the vertex as the middle point, such as ∠ABC.

  • Angle Relationships: Acute angles can interact with other angles, forming complementary angles (when combined with another angle to form a right angle) or supplementary angles (when combined with another angle to form a straight angle).


Obtuse and Acute Angle Differences

S.No

Category 

Obtuse Angle

Acute Angle

1.

Measurement

Greater than 90 degrees but less than 180 degrees

Less than 90 degrees

2.

Ray Configuration

One ray extends beyond the perpendicular position

Rays form a sharp V-shape from the same endpoint

3.

Properties

Provides insights into the properties of angles and shapes

Helps analyze the characteristics and relationships of angles and polygons

4.

Shape

Wider and more open compared to a right angle

Narrower and more compact compared to a right angle

5. 

Relationship to Right Angle

Larger than a right angle

Smaller than a right angle

6. 

Angle Relationships

Can form supplementary angles with other angles

Can form complementary angles with other angles


These differences highlight how obtuse and acute angles have distinct measurements, configurations, and effects on angle relationships and geometric properties.


Summary 

Obtuse and acute angles are two types of angles in geometry. Obtuse angles are angles that measure greater than 90 degrees but less than 180 degrees. They appear wider and more open than at a right angle. Examples include angles in triangles where one angle is greater than 90 degrees. Whereas, Acute angles are angles that measure less than 90 degrees. They appear narrower and more compact compared to a right angle. Examples include angles in equilateral triangles and angles formed by the hands of a clock when indicating specific times. Both obtuse and acute angles are fundamental concepts in geometry, and their measurements and properties play significant roles in understanding shapes, angles, and relationships.

WhatsApp Banner

FAQs on What's the Difference Between an Obtuse and an Acute Angle?

1. What is the difference between an acute and an obtuse angle?

An acute angle measures less than 90 degrees, while an obtuse angle is greater than 90 degrees but less than 180 degrees.

Key differences:

  • Acute angle: Less than 90°
  • Obtuse angle: More than 90° and less than 180°
  • Acute angles appear sharper, while obtuse angles look wider
  • Both are types of angles studied in geometry

2. What is an acute angle?

An acute angle is an angle that measures less than 90 degrees.

Features:

  • Always less than 90°
  • Smaller than a right angle
  • Common examples: 30°, 45°, and 60°
  • Often found in triangles and polygons

3. What is an obtuse angle?

An obtuse angle is an angle that measures more than 90 degrees but less than 180 degrees.

Key points:

  • Greater than 90°, smaller than 180°
  • Wider than a right angle
  • Common examples: 120°, 135°, 150°

4. How do you identify an acute and an obtuse angle visually?

To identify the type of angle:

  • Acute angles look sharp and are smaller than a right angle (less than 90°)
  • Obtuse angles look wider and open more than a right angle (more than 90°, but less than 180°)

5. Can a triangle have both acute and obtuse angles?

No, a triangle cannot have both acute and obtuse angles together.

Reason:

  • A triangle can have only one obtuse angle at most
  • The other two angles must be acute for the sum to be 180°
  • If a triangle has all angles less than 90°, it is called an acute triangle

6. What examples in daily life use acute and obtuse angles?

Examples of acute angles in real life include:

  • The tip of a slice of pizza
  • Scissors' pointed end
  • A house roof peak

Examples of obtuse angles include:

  • The angle when a book is opened wide
  • The hands of a clock at 10:15
  • A ramp gently sloping upwards

7. How do you measure an acute and an obtuse angle?

To measure any angle, use a protractor.

Steps:

  • Place the midpoint of the protractor at the angle's vertex
  • Align one side of the angle with the zero line
  • Read the measurement on the scale where the other side meets

An acute angle will show less than 90°, while an obtuse angle will show between 90° and 180°.

8. Can an angle be both acute and obtuse?

No, a single angle cannot be both acute and obtuse at the same time.

  • Acute angles are always below 90°
  • Obtuse angles are always between 90° and 180°
Each angle type is mutually exclusive in geometry.

9. Which triangles have obtuse angles?

A triangle with one obtuse angle is called an obtuse triangle.

  • Only one angle can be obtuse (more than 90°)
  • The other two angles will always be acute
  • Sum of all angles in any triangle: 180°

10. What is the sum of angles in a triangle and how do acute and obtuse angles fit in?

The sum of all three angles in a triangle is always 180 degrees.

  • A triangle may have all acute angles (acute triangle)
  • Or one obtuse angle and two acute angles (obtuse triangle)
  • It cannot have more than one obtuse angle

11. List the main types of angles with their degree ranges.

The main types of angles and their degree measures are:

  • Acute angle: less than 90°
  • Right angle: exactly 90°
  • Obtuse angle: more than 90°, less than 180°
  • Straight angle: exactly 180°
  • Reflex angle: more than 180°, less than 360°