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# Lines – Definition, Types, & Examples ### Key Concepts

• Lines
• Classification of Triangles
• Classification of Quadrilaterals

## Lines

### Introduction:

Definition

Line:

A line is a figure formed when two points are connected with minimum distance between them and have no ends on both sides.

A line AB  is represented by

AB↔

A real-life example of a line

Line Segment:

A line segment is part of a line that has a fixed endpoint on both the ends.

A line segment AB is represented by AB−

A real-life example of a line segment

Ray:

A ray is a part of a line that has only one fixed point, and the other point does not have any end.

A line segment AB  is represented by  AB→

A real-life example of a ray

### Types of lines:

Basically, lines are of 3 types:

1. Parallel lines
1. Intersecting lines
1. Perpendicular lines
1. Parallel lines

Two lines are said to be parallel lines if they lie in the same plane and never meet.

Parallel lines

Non- Parallel lines

A real-life example of parallel lines

1. Intersecting lines

If two lines meet at a point, they are said to be intersecting lines.

A real-life example of intersecting lines

Scissors, the two blades of the scissors intersect at each other to make it work effectively.

1. Perpendicular lines

When two lines intersect at an angle of 90o or at a right angle, then they are perpendicular to each other.

A real-life example of perpendicular lines

Clocks are the best examples to show perpendicular lines at 3 O’ clock and 9 O’ clock.

## Classification of Triangles

### Triangle (Definition)

A triangle is a closed shape with three angles, three sides and three vertices.

Triangles can be classified as:

• On the basis of angles
• On the basis of measurement of their sides

A real-life example of triangles

### Classification of Quadrilaterals

A quadrilateral is a closed two-dimensional shape that has 4 sides, 4 angles, and 4 vertices.

A real-life example of a quadrilateral

### Types of Quadrilaterals:

Quadrilaterals are classified based on their sides, angles, and diagonals.

A real-life example of types of quadrilaterals

## Exercise:

1. Find out the number of sleeping lines, slanting lines, curved lines, circles, square, triangle and rectangle in the figure below:
1. Is it possible to have an obtuse acute triangle? Explain.
2. What is true about all quadrilaterals?
3. What is the difference between a square, and a rhombus?
4. Can a trapezoid have perpendicular sides?
5. Classify each triangle by its sides, and then by its angles.
6. The blades of an open pair of scissors look like what pair of lines?
7. What geometric term could you use to describe the top, and bottom edges of a book?
8. How many acute angles are there in an equilateral triangle?
9. What kinds of triangles never have right angles?

### What we have learnt:

• Recognize and define lines, line segments and rays
• Understand parallel and perpendicular lines
• Understand triangles based on angles
• Understand triangles based on sides
• Learn quadrilaterals and classification of quadrilaterals
• Solve questions based on lines, angles, and shapes

### Concept Map:

Classification of Lines

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