Lines and Angles Class 9 Notes Maths - Chapter 6
What Are Lines And Angles ?
Collinear And Non-collinear Points
• If three or more points lies on the same line then they are called collinear points.
• It the points are not collinear then we can say they are non-collinear points.
• Two points are always collinear.
Parallel And Intesecting Lines
• Two lines are said to be intersecting, if they intersect each other at one point.
• Lines which do not intersect are called parallel lines.
An Important Fact
Lines which are parallel to the same line, are parallel to each other.
Some Important Facts
• If a ray stands on a line, then the sum of the adjacent angles so formed is 180°, i.e., the sum of the linear pair of angles is 180°.
• If two lines intersect each other, then the vertically opposite angles are equal.