CBSE Notes for Class 9 Maths Chapter 6 Lines And Angles

Class 9 Maths Chapter 6 Lines And Angles

Chapter 6 of Class 9, Lines and Angles, is a subsection of Geometry. It deals with various angles made by the interaction of lines and rays. The knowledge of this chapter builds a basis for the study of higher mathematics. Hence this chapter comes to be an essential one to enjoy the beauty of mathematics. But how do I cover the entire chapter for my examination? You can learn this chapter with the study material provided at GharPeShiksha. It contains the best Revision Notes, NCERT solutions, NCERT Exemplar Solutions, Previous Year Questions of this Chapter, Formulae Sheet, Model Answer Sheets designed by its expert teachers. The study material is updated each year as per the syllabus requirements and is consistent with the new exam pattern. It is an exclusive feature that the students can avail of at GharPeShiksha only.


Lines are the straight figures, made up of infinite points, extending infinitely in both the directions. They have negligible depth or width. There are four types of lines: horizontal line, vertical line, perpendicular, and parallel lines.
Note: When the lines or line segments intersect, then angles are formed.


  • An angle is a figure formed from the two rays emerging from a common endpoint.

Types of angles:

  • Acute angle- Angles less than 90
  • Obtuse angle- angles more than 90 but less than 180
  • Right angle- Angles equal to 90
  • Straight angle- Angles equal to 180
  • Reflex angle
  • Complementary angle
  • Supplementary angle

Vertically opposite angles

When two lines intersect each other, then the opposite angles are called vertically opposite angles. A pair of vertically opposite angles are always equal to each other.

When two lines intersect each other, then the opposite angles, formed due to intersection are called vertical angles or vertically opposite angles. A pair of vertically opposite angles are always equal to each other.

Corresponding angles

Converse of Corresponding angles

therefor, the line / m are parallel to each other.

Alternate angles

Converse of Alternate angles

Angle on the same side of transversal

NOTE: The converse is also true.

Important note:

Exterior angle theorem

This property is called exterior angle property of a triangle.


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