lightbulb Key Concepts

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1. Types of Angles

• Acute Angle: Less than 90°
• Right Angle: Exactly 90°
• Obtuse Angle: Greater than 90° but less than 180°
• Straight Angle: Exactly 180°
• Reflex Angle: Greater than 180° but less than 360°

2. Pairs of Angles

• Complementary: Sum is 90°
• Supplementary: Sum is 180°
• Adjacent: Share a common vertex and arm.
• Linear Pair: Adjacent angles whose non-common arms are opposite rays (sum is 180°).
• Vertically Opposite: Formed by intersecting lines; they are equal.

3. Parallel Lines and Transversal

When a transversal intersects two parallel lines:

• Corresponding angles are equal.
• Alternate interior angles are equal.
• Co-interior angles are supplementary (sum to 180°).