Parallel lines in shapes can form corresponding and alternate angles. ... Angles inside a shape are called interior angles. Interior angles in a triangle add up to 180°.

The interior angle and its corresponding exterior angle always add up to 180°. ... (alternate angles are equal) \(a + d + e = 180^\circ\) (angles on a straight line add up to 180°) ...

Class 9 Maths Chapter 6 Lines and Angles is available here for download in PDF format. We have provided here the latest edition of the chapter which is published by the NCERT on its official website.