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SAI InternationalSchool
CLASS - IX

Mathematics

CHAPTER-6: Lines and Angles
Lesson Notes

SUB TOPIC: PARALLEL LINES AND A TRANSVERSAL

Transversal:

A line which intersects two or more lines at distinct points is called a transversal.

Here, line ‘l’ is a transversal of the lines ‘m’ and ‘n’, respectively.
Line ‘l’ intersects m and n at P and Q respectively, then four angles are formed at each
of the points ‘P’ and ‘Q’ namely…
∠1, ∠2, ∠3,∠4, ∠5, ∠6, ∠7 and∠8 .
∠1, ∠2, ∠7 and ∠8are called exterior angles.
∠3, ∠4, ∠5 and ∠6 are called interior angles.
We classify these eight angles in the following groups.
(i) Corresponding angles.

 ∠1 and ∠5
 ∠2 and ∠6
 ∠4 and ∠8
 ∠3 and ∠7

(ii) Alternate interior angles

 ∠4 and ∠6

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