NCERT Class 9 Mathematics Textbook for Blind Students made Screen Readable by Professor T K Bansal.

In this chapter, we have studied the following points:

1.
If a ray stands on a line, then the sum of the two adjacent angles so formed is 180° and vice-versa. This property is called the Linear pair axiom.

2.
If two lines intersect each other, then the vertically opposite angles are equal.

3.
If a transversal intersects two parallel lines, then
(i) each pair of corresponding angles is equal,
(ii) each pair of alternate interior angles is equal,
(iii) each pair of interior angles on the same side of the transversal is supplementary.

4.
If a transversal intersects two lines such that, either
(i) any one pair of corresponding angles is equal, or
(ii) any one pair of alternate interior angles is equal, or
(iii) any one pair of interior angles on the same side of the transversal is supplementary,
then the lines are parallel.

5.
Lines which are parallel to a given line are parallel to each other.

6.
The sum of the three angles of a triangle is 180°.

7.
If a side of a triangle is produced, the exterior ∠so formed is equal to the sum of the two interior opposite angles.

Acknowledgements

We at ‘Blind to Visionaries Trust’, are thankful to
1. Dr. T K Bansal, M.Tech, PhD (IIT Delhi), P.D.F (University of oxford) and former senior lecture from IIT Kharagpur, for planning, organizing and describing this lesson for visually impaired students
2. Mr. Arun Kumar for typing and setting this lesson with full devotion and dedication, and for helping Dr T K Bansal in writing the alt text for each and every figure.
3. In case you suggest us any improvement or can point us any mistakes in this chapter your name will also be added to this list of contributors
4. Do you know that the readers of this chapter are also the contributors! In case you take benefit of our efforts and encourage us by sending your comments, your name will also be added to this list.

End of Chapter 6