Angles Basics

Understanding Angles

An angle is formed when two rays meet at a common endpoint called the vertex. Angles are measured in degrees (°).

Here are some key points about angles:

• Acute Angle: An angle less than 90°.
• Right Angle: An angle exactly 90°.
• Obtuse Angle: An angle greater than 90° but less than 180°.
• Straight Angle: An angle exactly 180°.
• Reflex Angle: An angle greater than 180°.

Angles on Parallel Lines

When a pair of parallel lines is intersected by a transversal, several angles are formed. Understanding these angles is crucial:

• Corresponding Angles: Angles in matching corners when a transversal crosses parallel lines. They are equal.
• Alternate Interior Angles: Angles on opposite sides of the transversal but inside the parallel lines. They are equal.
• Alternate Exterior Angles: Angles on opposite sides of the transversal but outside the parallel lines. They are equal.
• Co-Interior Angles: Angles on the same side of the transversal and inside the parallel lines. They add up to 180°.

Bisecting Angles

To bisect an angle means to divide it into two equal parts. This can be done using a compass and a ruler.