**Lines and Angles**

Angle is the amount of turn between two straight lines that have a common end point (the vertex). A line is a collection of points along a straight path that goes on and on in opposite directions. A line has no endpoints.Watch Lines Angles Videos to learn more.

A true line in geometry is a straight bar that keeps going and going in both directions. We label lines by labeling any two points on the line and call the line by those two points.

**(a) Segment:- **– A part of line with two end points is called a line-segment.

**(b) Ray:- **– A part of a line with one end-point is called a ray.

**(c) Collinear points:** – If three or more points lie on the same line, then they are called collinear points, otherwise they are called non-collinear points.

**(d) Angle:-** An angle is formed by two rays originating from the same end point.

The rays making an angle are called the arms and the end-points are called the vertex.

**Types of Angles:**–

**(i) Acute angle:** -whose measure lies between 0° and 90°.

**(ii) Right angle:** -whose measure is equal to 90°.

**(iii) Obtuse angle:** – whose measure lies between 90° and 180°.

**(iv) Straight angle:** – The measure of a straight angle is 180°.

**(v) Reflex angle:** – which is greater than 180° and less than 360°.

**(vi) Complimentary angle:** – whose sum is 90°.

**(vii) Supplementary angle:** – Two angles whose sum is 180º.

**(viii) Adjacent angle:** – Two angles are adjacent, if they have a common vertex, common arm and their non-common arms are on different sides of the common arm.

**(ix) Linear pair of angles:** – If the sum of two adjacent angles is 180º, then their non-common lines are in the same straight line and two adjacent angles form a linear pair of angles.

**Lines Angles Videos**

Useful for CBSE, ICSE, NCERT & International Students

Grade : 9

Subject : Maths

Lesson : Lines and Angles

Topic: Lines Angles Videos

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