Lines and Angles
When two lines cross or a transversal cuts parallels, the resulting angles obey strict rules. Chapter 6, Lines and Angles, of the NCERT Mathematics textbook for Class 9 proves these rules instead of merely stating them. You will establish which angle pairs are equal when lines are parallel and prove the converse, then derive the angle-sum property of a triangle with a neat construction. Exercises ask you to supply missing reasons step by step, turning familiar facts into theorems with proper proofs.
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