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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. 

Line

A line AB  is represented by

AB↔

A real-life example of a line 

Fig 4 (Roadway lines)

Line Segment: 

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

Line Segment: 

A line segment AB is represented by AB−

A real-life example of a line segment 

Fig 6 (Soccer ground)

Ray: 

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

Ray: 

A line segment AB  is represented by  AB→

A real-life example of a ray 

Fig 8 (Torchlight rays and beams)

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 

Parallel lines 

Non- Parallel lines 

Non- Parallel lines 

A real-life example of parallel lines 

Fig 10 (Railway tracks)
  1. Intersecting lines 

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

Fig 11 (Intersecting lines)

A real-life example of intersecting lines 

Fig 12 (Scissor)

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. 

Fig 13 (Perpendicular lines)
Fig 14 (Non Perpendicular lines)

A real-life example of perpendicular lines 

Fig 14 (Clock)

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.  

Triangle (Definition) 

Triangles can be classified as: 

  • On the basis of angles 
  • On the basis of measurement of their sides 
Fig 16 (Types of triangles)

A real-life example of triangles 

Fig 17 (Sailing boat)

Classification of Quadrilaterals 

Quadrilateral 

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

Quadrilateral 

A real-life example of a quadrilateral 

Fig 19 (Boxer fight Cancun box quadrilateral)

Types of Quadrilaterals: 

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

Types of Quadrilaterals: 

A real-life example of types of quadrilaterals 

chess
house
sign board
paltter

Exercise:

  1. Find out the number of sleeping lines, slanting lines, curved lines, circles, square, triangle and rectangle in the figure below:
exercise
  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 

lines
All About Lines 

Classification of Quadrilaterals 

Classification of Quadrilaterals 

Classification of Triangles 

Classification of Triangles 

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