**Class 9 Maths – Chapter 6: Lines and Angles (Easy Notes + Important Questions)**
1. Basic Terms:
- Line, Line Segment, Ray, Collinear Points.
2. Types of Angles:
Acute (<90°), Right (90°), Obtuse (90°–180°), Straight (180°), Reflex (180°–360°), Complete (360°).
3. Angle Pair Properties:
- Linear Pair: Sum = 180°
- Vertically Opposite Angles: Equal
- Corresponding Angles: Equal (parallel lines)
- Alternate Interior Angles: Equal
- Alternate Exterior Angles: Equal
- Co-interior Angles: Sum = 180°
4. Important Theorems:
- VOA are equal.
- Corresponding angles are equal (parallel lines).
- Alternate interior angles are equal.
- Co-interior angles sum to 180°.
5. Extra Important Questions (With Solutions):
Q1. If one angle of a linear pair is 70°, find the other.
Ans: 110°
Q2. Two angles form a linear pair: 3x and 2x + 10°. Find x.
Ans: x = 34°
Q3. One angle formed by two intersecting lines is 125°. Find its vertically opposite angle.
Ans: 125°
