**Lines And Angles:** In geometry, lines are figures that are made up of infinite points extending indefinitely in both directions. Lines are straight and have negligible depth or width. There are a variety of lines you will learn about, such as perpendicular lines, intersecting lines, transversal lines, etc. An angle is a figure in which two rays emerge from a common point. You may also come across alternate and corresponding angles in this field.Â Â Geometry shapes and their properties are the most practical branch of mathematics. Mostly this concept has been taught in Class 7 and Class 9.

## Lines and Angles – Definition And Properties

Here, the basic definitions and properties of lines and also for angles are given. It will give the students a basic knowledge of these geometrical terms.

Lines are basically categorized as:

- Line segment
- Ray

Angles are basically classified as:

- Acute Angle(<90Â°)
- Right Angle(=90Â°)
- Obtuse Angle(>90Â°)
- Straight Angle(=180Â°)

Based on concepts or operations performed on lines, they are;

- Parallel Lines
- Perpendicular Lines
- Transversal

And based on the relation between two angles, conceptual wise, they are;

- Supplementary Angles
- Complementary Angles
- Adjacent Angles
- Vertically Opposite Angles

### Line Segment

A line segment is a part of a line with two end-points. It is the shortest distance between two points and has a fixed length.

### Ray

A ray is a part of a line, which has a starting point and extendsÂ infinitely in one direction.

### Perpendicular Lines

When two lines form a right angle with each other, by meeting at a single point, are called perpendicular lines. In the figure, you can see, lines AB and CD are perpendicular to each other.

### Parallel Lines

Two lines are said to be parallel when they do not meet at any point in a plane or which do not intersects each other. In the figure, lines PQ and RS are parallel to each other.

### Transversal Line

When a line intersects two lines at distinct points, it is called a transversal. In the figure, a transversal *l* is intersecting two lines at point P and Q.

### Properties of Lines

- Collinear points are a set of three or more points which lie on the same line.
- The points which do not lie on the same line are called non-collinear points.

**Note:** Three points can be either collinear or non-collinear, but not both together at the same time.

### Acute Angle

If the inclination between the arms is less than a right angle, it is called an acute angle.

### Obtuse Angle

If the inclination between the arms is more than a right angle, it is called an obtuse angle.

### Right Angle

If the arms form an angle of 90 degrees between them, it is called a right angle.

### Straight Angle

If the arms form an angle of 180 degrees between them, it is called a straight angle.

### Complementary Angles

Two angles which sum up to 90 degrees are called complementary angles.

### Supplementary Angles

Two angles which sum up to 180 degrees are called supplementary angles.

### Adjacent Angles

Two angles which have a common side and a common vertex are called adjacent angles. In the following figure, âˆ Î± and âˆ Î² are adjacent angles.

**Vertically Opposite Angles**

Two angles which are formed, opposite to each other, when two lines intersect at a common point or vertex, are called vertically opposite angles. In the figure, given below;

âˆ POR =Â âˆ SOQ andÂ âˆ POS =Â âˆ ROQ

### Properties of Angles

- An angle is a figure in which two rays emerge from a common point. This point is called the vertex of the angle and the two rays forming the angle are called its arms or sides.
- An angle which is greater than 180 degrees but less than 360 degrees is called a reflex angle.
- If two adjacent angles add up to 180 degrees, they form a linear pair of angles. In the following figure, âˆ a and âˆ b form a linear pair.

- When two lines intersect each other, the two opposite pairs of angles formed are called vertically opposite angles. In the following figure, âˆ A and âˆ B are vertically opposite angles. Another pair is âˆ C and âˆ D.

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## Frequently Asked Questions on Lines And Angles

### What are the five types of Angles?

The five types of angles are:

- Acute Angle
- Right Angle
- Obtuse Angle
- Straight Angle
- Reflex Angle

### What are the properties of Lines and Angles?

If two parallel lines are intersected by a transversal then:

- Its vertically opposite angles are always equal
- Its corresponding angles are equal
- Its alternate exterior and interior angles are equal

### What are Lines and its types?

Lines are figures that are made up of infinite points extending indefinitely in both directions. The types of lines are:

- Horizontal lines
- Vertical lines
- Parallel lines
- Perpendicular lines

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