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Angles and Lines
Revision Notes
Key Points
- Types of angles: acute, obtuse, right, reflex
- Parallel lines and the angles they create (corresponding, alternate interior, alternate exterior, co-interior)
- Perpendicular lines and right angles
- Vertically opposite angles, supplementary angles, and complementary angles
Types of Angles
- **Acute Angle**: An angle less than 90 degrees.
- **Obtuse Angle**: An angle greater than 90 degrees but less than 180 degrees.
- **Right Angle**: An angle of exactly 90 degrees.
- **Reflex Angle**: An angle greater than 180 degrees but less than 360 degrees.
Parallel Lines
Parallel lines are two or more lines that are equidistant from each other and never intersect. When a transversal line (a line that intersects two or more other lines) crosses parallel lines, it creates corresponding angles, alternate interior angles, alternate exterior angles, and co-interior angles.
Perpendicular Lines
Perpendicular lines are two lines that intersect at a right angle (90 degrees).
Angle Relationships
- **Vertically Opposite Angles**: Angles that are opposite each other when two lines intersect. They are always equal in measure.
- **Supplementary Angles**: Two angles that add up to 180 degrees.
- **Complementary Angles**: Two angles that add up to 90 degrees.