NCERT Solutions for Class 7 Maths Chapter 12 Symmetry

 

NCERT Solutions for Class 7 Maths Chapter 12 Symmetry

Exercise 12.1 

1. Copy the figures with punched holes and find the axes of symmetry for the following:

(a)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 1

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 2

(b)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 3

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 4

(c)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 5

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 6

(d)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 7

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 8

(e)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 9

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 10

 

(f)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 11

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 12

(g)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 13

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 14

(h)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 15

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 16

(i)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 17

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 18

(j)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 19

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 20

(k)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 21

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 22

(l)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 23

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 24

2. Given the line(s) of symmetry, find the other hole(s):

(a)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 25

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

So, other hole is shown in the figure below.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 26

 

(b)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 27

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

So, other hole is shown in the figure below.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 28

(c)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 29

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

So, other hole is shown in the figure below.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 30

(d)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 31

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

So, other hole is shown in the figure below.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 32

(e)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 33

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

So, other hole is shown in the figure below.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 34

3. In the following figures, the mirror line (i.e., the line of symmetry) is given as a dotted line. Complete each figure performing reflection in the dotted (mirror) line. (You might perhaps place a mirror along the dotted line and look into the mirror for the image). Are you able to recall the name of the figure you complete?

(a)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 35

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 36

Name of the figure is square.

(b)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 37

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 38

Name of the figure is triangle.

(c)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 39

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 40

Name of the figure is rhombus.

(d)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 41

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 42

Name of the figure is circle.

(e)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 43

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 44

Name of the figure is pentagon.

(f)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 45

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 46

Name of the figure is octagon.

4. The following figures have more than one line of symmetry. Such figures are said to have multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 47

Identify multiple lines of symmetry, if any, in each of the following figures:

(a)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 48

Solution:-

Figure given has 3 lines of symmetry.

So, it has multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 49

(b)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 50

Solution:-

Figure given has 2 lines of symmetry.

So, it has multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 51

(c)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 52

Solution:-

Figure given has 3 lines of symmetry.

So, it has multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 53

(d)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 54

Solution:-

Figure given has 2 lines of symmetry.

So, it has multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 55

(e)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 56

Solution:-

Figure given has 4 lines of symmetry.

So, it has multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 57

(f)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 58

Solution:-

Figure given has only 1 line of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 59

(g)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 60

Solution:-

Figure given has 4 lines of symmetry.

So, it has multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 61

(h)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 62

Solution:-

Figure given has 6 lines of symmetry.

So, it has multiple lines of symmetry.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 63

5. Copy the figure given here.

Take any one diagonal as a line of symmetry and shade a few more squares to make the figure symmetric about a diagonal. Is there more than one way to do that? Will the figure be symmetric about both the diagonals?

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 64

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 65

By observing the above figure,

Yes, the figure will be symmetrical about both diagonals.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 66

By observing the above figure,

Yes, the figure can be made symmetrical by more than one way.

6. Copy the diagram and complete each shape to be symmetric about the mirror line(s):

(a)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 67

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 68

(b)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 69

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 70

(c)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 71

Solution:-

The concept of line of 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. A mirror line, thus helps to visualise a line of symmetry.

While dealing with mirror reflection, care is needed to note down the left-right changes in the orientation.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 72

7. State the number of lines of symmetry for the following figures:

(a) An equilateral triangle

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

An equilateral triangle has 3 lines of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 73

(b) An isosceles triangle

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

An isosceles triangle has 1 lines of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 74

(c) A scalene triangle

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A scalene triangle has no line of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 75

(d) A square

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A square has 4 lines of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 76

(e) A rectangle

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A rectangle has 2 lines of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 77

(f) A rhombus

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A rhombus has 2 lines of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 78

(g) A parallelogram

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A parallelogram has no line of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 79

(h) A quadrilateral

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A quadrilateral has no line of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 80

(i) A regular hexagon

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A regular hexagon has 6 lines of symmetry is shown in the figure below,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 81

(j) A circle

Solution:-

A figure has a line of symmetry, if there is a line about which the figure may be folded so that the two parts of the figure will coincide.

A circle has infinite lines of symmetry,

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 82

8. What letters of the English alphabet have reflectional symmetry (i.e., symmetry related to mirror reflection) about.

(a) a vertical mirror (b) a horizontal mirror

(c) both horizontal and vertical mirrors

Solution:-

(a) a vertical mirror

The English alphabet have reflection symmetry about a vertical mirror are, A, H, I, M, O, T, U, V, W, X, Y

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 83

(b) a horizontal mirror

The English alphabet have reflection symmetry about a horizontal mirror are, B, C, D, E, H, I, K, O, X

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 84

(c) both horizontal and vertical mirrors

The English alphabet have reflection symmetry about both horizontal and vertical mirrors are, H, I, O, X

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 85

9. Give three examples of shapes with no line of symmetry.

Solution:-

A shape has a no line of symmetry, if there is no line about which the figure may be folded and also parts of the figure will not coincide.

A scalene triangle, a quadrilateral and a parallelogram

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 86

10. What other name can you give to the line of symmetry of

(a) an isosceles triangle?

Solution:-

The other name to the line of symmetry of an isosceles triangle is median or altitude.

(b) a circle?

The other name to the line of symmetry of a circle is diameter.


Exercise 12.2

1. Which of the following figures have rational symmetry of order more than 1?

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 87

Solution:-

(a)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 88

So, the above figure has its rotational symmetry as 4.

(b)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 89

So, the above figure has its rotational symmetry as 3.

(c) So, the given figure has only one rotational symmetry.

NCERT Solutions for Class 7 Maths Chap 14 Image 1

(d)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 90

So, the above figure has its rotational symmetry as 2.

(e)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 91

So, the above figure has its rotational symmetry as 3.

(f)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 92

So, the above figure has its rotational symmetry as 4.

By observing all the figures (a), (b), (c), (d), (e) and (f) have rotational symmetry of order more than 1.

2. Give the order of rotational symmetry for each figure:

(a)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 93

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 94

The above figure has its rotational symmetry as 2.

(b)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 95

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 96

The above figure has its rotational symmetry as 2.

(c)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 97

Solution:-

NCERT Solutions for Class 7 Maths Chap 14 Image 2

The above figure has its rotational symmetry as 3.

(d)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 99

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 100

The above figure has its rotational symmetry as 4.

(e)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 101

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 102

The above figure has its rotational symmetry as 4.

(f)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 103

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 104

The above figure has its rotational symmetry as 5.

(g)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 105

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 106

The above figure has its rotational symmetry as 6.

(h)

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 107

Solution:-

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 108

The above figure has its rotational symmetry as 3.


Exercise 12.3 

1. Name any two figures that have both line symmetry and rotational symmetry.

Solution:-

Equilateral triangle and circle.

2. Draw, wherever possible, a rough sketch of

(i) a triangle with both line and rotational symmetries of order more than 1.

Solution:-

A triangle with both line and rotational symmetries of order more than 1 is an equilateral triangle.

Line symmetry

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 109

Rotational symmetry

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 110

(ii) a triangle with only line symmetry and no rotational symmetry of order more than 1.

Solution:-

A triangle with only line symmetry and no rotational symmetry of order more than 1 is isosceles triangle.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 111

(iii) a quadrilateral with a rotational symmetry of order more than 1 but not a line symmetry.

Solution:-

A quadrilateral with a rotational symmetry of order more than 1 but not a line symmetry is not possible to draw. This is because a quadrilateral with a line symmetry may have rotational symmetry of order one but not more than one.

(iv) a quadrilateral with line symmetry but not a rotational symmetry of order more than 1.

Solution:-

A quadrilateral with line symmetry but not a rotational symmetry of order more than 1 is a rhombus.

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 112

3. If a figure has two or more lines of symmetry, should it have rotational symmetry of order more than 1?

Solution:-

Yes. If a figure has two or more lines of symmetry, then it will have rotational symmetry of order more than 1.

4. Fill in the blanks:

ShapeCentre of RotationOrder of RotationAngle of Rotation
Square
Rectangle
Rhombus
Equilateral Triangle
Regular Hexagon
Circle
Semi-circle

Solution:-

ShapeCentre of RotationOrder of RotationAngle of Rotation
SquareIntersecting point of diagonals490o
RectangleIntersecting point of diagonals2180o
RhombusIntersecting point of diagonals2180o
Equilateral TriangleIntersecting point of medians3120o
Regular HexagonIntersecting point of diagonals660o
CircleCentreInfiniteEvery angle
Semi-circleMid-point of diameter1360o

5. Name the quadrilaterals which have both line and rotational symmetry of order more than 1.

Solution:-

The quadrilateral which have both line and rotational symmetry of order more than 1 is a square.

Line symmetry:

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 113

Rotational symmetry:

NCERT Solutions for Class 7 Maths Chapter 14 Symmetry Image 114

6. After rotating by 60° about a centre, a figure looks exactly the same as its original position. At what other angles will this happen for the figure?

Solution:-

The other angles are, 120°, 180°, 240°, 300°, 360°

So, the figure is said to have rotational symmetry about same angle as the first one. Hence, the figure will look exactly the same when rotated by 60° from the last position.

7. Can we have a rotational symmetry of order more than 1 whose angle of rotation is

(i) 45°?

Solution:-

Yes. We can have a rotational symmetry of order more than 1 whose angle of rotation is 45o.

(ii) 17°?

Solution:-

No. We cannot have a rotational symmetry of order more than 1 whose angle of rotation is 17o.

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