Mathematics · Class 9
Lines and Angles
Angle relationships with parallel lines and triangle angle sums.
3 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Lines and Angles studies angle types, pairs formed by intersecting lines and transversals, and properties when lines are parallel. These results are used throughout triangles and quadrilaterals.
Types of Angles
- Acute (< 90°), right (= 90°), obtuse (90°–180°), straight (= 180°)
- Complementary angles sum to 90°; supplementary sum to 180°
- Vertically opposite angles are equal
- Linear pair: adjacent angles on a line sum to 180°
Parallel Lines and Transversal
- Corresponding angles are equal
- Alternate interior angles are equal
- Co-interior (same-side interior) angles are supplementary
- Converse statements help prove lines parallel
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Example 1: Vertically opposite
Two lines intersect. One angle is 65°. Find vertically opposite angle.
- 1Vertically opposite angles are equal
Answer
65°
Example 2: Parallel lines
Transversal cuts parallel lines. Corresponding angle = 110°. Find alternate interior angle.
- 1Corresponding angles equal → 110°
- 2Alternate interior equals corresponding angle
Answer
110°
Key Points to Remember
- ✓ Angle sum on straight line = 180°
- ✓ Around a point, angles sum to 360°
- ✓ If corresponding angles equal, lines are parallel
Exam Tips
- • Mark equal angles on diagram
- • State reason (corresponding/alternate) in proofs
- • Check if angles form linear pair
Practice MCQs — Lines and Angles
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Complement of 35° is: