## Class 9 Maths Chapter 6 Lines And Angles

**LINE**

Lines are the straight figures, made up of infinite points, extending infinitely in both the directions. They have negligible depth or width. There are four types of lines: horizontal line, vertical line, perpendicular, and parallel lines.**Note**: When the lines or line segments intersect, then angles are formed.

**ANGLE**

- An angle is a figure formed from the two rays emerging from a common endpoint.

**Types of angles:**

- Acute angle- Angles less than 90
- Obtuse angle- angles more than 90 but less than 180
- Right angle- Angles equal to 90
- Straight angle- Angles equal to 180
- Reflex angle
- Complementary angle
- Supplementary angle

**Vertically opposite angles**

When two lines intersect each other, then the opposite angles are called vertically opposite angles. A pair of** vertically opposite angles** are always equal to each other.

When two lines intersect each other, then the opposite angles, formed due to intersection are called **vertical angles** or **vertically opposite angles**. A pair of vertically opposite angles are always equal to each other.

**Corresponding angles**

**Converse of Corresponding angles**

therefor, the line / m are parallel to each other.

**Alternate angles**

**Converse of Alternate angles**

**Angle on the same side of transversal**

**NOTE**: The converse is also true.**ANGLE SUM PROPERTY OF A TRIANGLE**

**Important note:**

**Exterior angle theorem**

**This property is called exterior angle property of a triangle.Example**:

**NOTE**: