Types of Angles

Special Angles

1. Straight Angle

If you make a half turn, the two rays lie in a straight line pointing in opposite directions.

• Measure: Exactly $180^\circ$.
• It looks like a straight line.

2. Right Angle

If you make a quarter turn (half of a straight angle), you get a right angle.

• Measure: Exactly $90^\circ$.
• It forms an ‘L’ shape.
• Two lines that meet at a right angle are called perpendicular lines.

Classifying by Measure

We classify other angles based on how they compare to Right and Straight angles.

3. Acute Angle

• Description: Smaller than a right angle (sharp).
• Measure: Greater than $0^\circ$ and less than $90^\circ$.

4. Obtuse Angle

• Description: Greater than a right angle but less than a straight angle (blunt).
• Measure: Greater than $90^\circ$ and less than $180^\circ$.

5. Reflex Angle

• Description: Greater than a straight angle but less than a full turn.
• Measure: Greater than $180^\circ$ and less than $360^\circ$.