NCERT Class 7 Maths Symmetry

Scroll down for PDF

NCERT Class 7 Maths Symmetry. Download NCERT Chapters and Books in pdf format. Easy to print and read. Copies of these textbooks may be downloaded and used as textbooks or for reference. Refer to other chapters and books at other links (NCERT now providing you soft copies of all textbooks of all subjects from class first to twelfth online). 

Symmetry

14.1 INTRODUCTION

Symmetry is an important geometrical concept, commonly exhibited in nature and is used almost in every field of activity. Artists, professionals, designers of clothing or jewellery, car manufacturers, architects and many others make use of the idea of symmetry. The beehives, the flowers, the tree-leaves, religious symbols, rugs, and handkerchiefs — everywhere you find symmetrical designs.

You have already had a ‘feel’ of line symmetry in your previous class. A figure has a line symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide. You might like to recall these ideas. Here are some activities to help you. Enjoy identifying lines (also called axes) of symmetry in the designs you collect. Let us now strengthen our ideas on symmetry further. Study the following figures in which the lines of symmetry are marked with dotted lines. [Fig 14.1 (i) to (iv)]

14.2 LINES OF SYMMETRY FOR REGULAR POLYGONS

You know that a polygon is a closed figure made of several line segments. The polygon made up of the least number of line segments is the triangle. (Can there be a polygon that you can draw with still fewer line segments? Think about it). A polygon is said to be regular if all its sides are of equal length and all its angles are of equal measure. Thus, an equilateral triangle is a regular polygon of three sides. Can you name the regular polygon of four sides?

An equilateral triangle is regular because each of its sides has same length and each of its angles measures 60° (Fig 14.2).

A square is also regular because all its sides are of equal length and each of its angles is a right angle (i.e., 90°). Its diagonals are seen to be perpendicular bisectors of one another (Fig 14.3). If a pentagon is regular, naturally, its sides should have equal length. You will, later on, learn that the measure of each of its angles is 108° (Fig 14.4). A regular hexagon has all its sides equal and each of its angles measures 120°. You will learn more of these figures later (Fig 14.5). The regular polygons are symmetrical figures and hence their lines of symmetry are quite interesting,

Each regular polygon has as many lines of symmetry as it has sides [Fig 14.6 (i) - (iv)]. We say, they have multiple lines of symmetry.

Perhaps, you might like to investigate this by paper folding. Go ahead!

The concept of line symmetry is closely related to mirror reflection. A shape has line symmetry when one half of it is the mirror image of the other half (Fig 14.7). A mirror line, thus, helps to visualise a line of symmetry (Fig 14.8). 

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation, as seen in the figure here (Fig 14.9).

The shape is same, but the other way round! Play this punching game! Fold a sheet into two halves Punch a hole two holes about the symmetric fold.

The fold is a line (or axis) of symmetry. Study about punches at different locations on the folded paper and the corresponding lines of symmetry (Fig 14.10).


Please refer to attached file for NCERT Class 7 Maths Symmetry

Tags: 


Click on the text For more study material for Mathematics please click here - Mathematics

Latest NCERT & CBSE News

Read the latest news and announcements from NCERT and CBSE below. Important updates relating to your studies which will help you to keep yourself updated with latest happenings in school level education. Keep yourself updated with all latest news and also read articles from teachers which will help you to improve your studies, increase motivation level and promote faster learning

Sample Papers for Class 10 Boards 2020

CBSE has recently released the Class 10 Sample Papers for Board exams which are to be held in March 2020. The sample papers have been for class 10 for all subjects along with the suggested marking scheme. CBSE releases these suggested papers every year so that the...

CBSE Board Practical Exam 2020

CBSE Board Practical Exam 2020: Important changes in date sheet, internal/external examiners and more Are you doing preparations for class 10 and 12 CBSE board exams? If yes, then you have to see what major changes CBSE has brought in the CBSE date sheet for class 10...

CBSE schools to have sports period daily for classes 1 to 12

CBSE schools to have sports period daily for classes 1 to 12, new curriculum introduced All work and no play makes a child dull. Nowadays students have a very hectic schedule so that they cannot take out time to play games and gently start ignoring sports. Therefore,...

CBSE Board Exams Changes to be implemented in exam pattern

CBSE Board Exams Class 10 & 12 2020: Changes to be implemented in exam pattern Are you appearing for the CBSE Class 10 and 12 Board Exams 2020? If yes, then you have to check out what CBSE has brought the major changes for the CBSE class 10 and 12 board exams 2020...

JEE Main registration 2020 List of qualifying exams

JEE Main registration 2020: List of qualifying exams The process of JEE (Joint Entrance Examination) Main has already been started from September 3, 2019, on the official website of JEE, i.e. jeemain.nic.in. The interested and eligible students can also apply for JEE...

CBSE and Microsoft join hands to build capacity for AI learning for schools

Central Board of Secondary Education and Microsoft join hands to build capacity for AI learning for schools : The officials from the Central Board of Secondary Education have announced that they have partnered with Microsoft India to conduct several capacity building...

×
Studies Today