Table of Contents:
- Definition
- Types of Angles
- Interior and Exterior Angles
- Positive and Negative Angles
- Parts of Angles
- Measurement
- In Degrees
- In Radians
- Gradian
- Practice Problems
- FAQs
Definition
An angle is a geometrical shape formed by connecting two rays at their endpoints. Angles can be represented by three letters, where the middle letter indicates the vertex. Common symbols used for angles include Greek letters such as θ, α, β, etc. For instance, ∠ABC denotes angle B.
Types of Angles
In geometry, there are primarily six types of angles, each with distinct properties:
Type of Angle | Description |
---|
Acute Angle | Less than 90° |
Obtuse Angle | Greater than 90° but less than 180° |
Right Angle | Exactly 90° |
Straight Angle | Exactly 180° |
Reflex Angle | Greater than 180° but less than 360° |
Full Rotation | Exactly 360° |
Interior and Exterior Angles
In polygons such as triangles, quadrilaterals, pentagons, and hexagons, we distinguish between interior and exterior angles. Interior angles are located within the polygon, while exterior angles are formed outside, between a side and a line extended from an adjacent side.
Positive & Negative Angles
Positive angles are measured in the anti-clockwise direction, while negative angles are measured clockwise.
Parts of Angles
- Vertex: The point where the two rays meet.
- Arms: The sides of the angle formed by the rays.
- Initial Side: The reference line for measuring angles.
- Terminal Side: The ray where angle measurement ends.
Angle Measurement
Angles can be measured using various units:
Degree of an Angle
Represented by °, degrees originated from the Babylonian base-60 system. A complete rotation is 360°. One degree is further divided into minutes (1' = 1/60°) and seconds (1" = 1/60'). Thus:
1° = 60′ = 3600”
Radian of an Angle
The radian is the SI unit for angles, commonly used in calculus. It is defined by the arc length on a unit circle. One complete circle is equivalent to 2π radians. Therefore:
1 radian = 180°/π
Gradian of an Angle
Gradians, also known as gon or grade, measure angles where a complete rotation equals 400 gradians.
Practice Problems
Use a protractor to draw angles measuring:
- 45 degrees
- 55 degrees
- 70 degrees
- 90 degrees
- 130 degrees
Frequently Asked Questions – FAQs
- What is an angle? An angle is a geometric figure formed by two rays meeting at a vertex.
- What are the six types of angles? The six major types are Acute, Obtuse, Right, Straight, Reflex, and Full rotation.
- How are angles measured? Angles are measured in degrees using a protractor.
- What is 60 degrees in radians? 60 degrees equals π/3 radians.
- What is a zero angle? An angle measuring zero degrees is known as a zero angle.
- Can a triangle have two 90-degree angles? No, a triangle cannot have two right angles as the total sum of angles must equal 180 degrees.