RD Sharma solution class 7 chapter 18 Symmetry Objective Type Questions

Objective Type Questions

Page-18.17

Question 1:

Give the order of rotational symmetry for each of the following figures when rotated about the marked point (x):

Answer 1:

(i) The given figure has its rotational symmetry as 4.
(ii) The given figure has its rotational symmetry as 3.
(iii) The given figure has its rotational symmetry as 3.
(iv) The given figure has its rotational symmetry as 4.
(v) The given figure has its rotational symmetry as 2.
(vi) The given figure has its rotational symmetry as 4.
(vii) The given figure has its rotational symmetry as 5.
(viii) The given figure has its rotational symmetry as 6.
(ix) The given figure has its rotational symmetry as 3.

Question 2:

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

Answer 2:

An equilateral triangle and a square have both lines of symmetry and rotational symmetry.

Question 3:

Give an example of a figure that has a line of symmetry but does not have rotational symmetry.

Answer 3:

A semicircle and an isosceles triangle have a line of symmetry but do not have rotational symmetry.

Question 4:

Give an example of a geometrical figure which has neither a line of symmetry nor a rotational symmetry.

Answer 4:

A scalene triangle has neither a line of symmetry nor a rotational symmetry.

Question 5:

Give an example of a letter of the English alphabet which has (i) no line of symmetry and (ii) rotational symmetry of order 2.

Answer 5:

(i) The letter of the English alphabet which has no line of symmetry is Z.
(ii) The letter of the English alphabet which has rotational symmetry of order 2 is N.

Question 6:

What is the line of symmetry of a semi-circle? Does it have rotational symmetry?

Answer 6:

A semicircle (half of a circle) has only one line of symmetry .
In the figure, there is one line of symmetry. The figure is symmetric along the perpendicular bisector l of the diameter XY.


A semi-circle does not have any rotational symmetry.

Question 7:

Draw, whenever possible, a rough sketch of
(i) a triangle with both line and rotational symmetries.
(ii) a triangle with only line symmetry and no rotational symmetry.
(iii) a quadrilateral with a rotational symmetry but not a line of symmetry.
(iv) a quadrilateral with line symmetry but not a rotational symmetry.

Answer 7:

(i) An equilateral triangle has 3 lines of symmetry and a rotational symmetry of order 3.
   

(ii) An isosceles triangle has only 1 line of symmetry and no rotational symmetry.
     
(iii) A parallelogram is a quadrilateral which has no line of symmetry but a rotational symmetry of order 2.
     
(iv) A kite is a quadrilateral which has only one line of symmetry and no rotational symmetry.
    

Question 8:

Fill in the blanks:

Figures Centre of rotation Order of rotation Angle of rotation
Square      
Rectangle      
Rhombus      
Equilateral triangle      
Regular hexagon      
Circle      
Semi-circle      

Answer 8:

Page-18.18

Question 3:

Which of the following has an infinite number of lines of symmetry?
(a) Equilateral triangle
(b) Isosceles triangle
(c) Regular hexagon
(d) Circle

Answer 3:

A circle has infinite number of lines of symmetry

Hence, the correct answer is option (d).

Question 4:

Which of the following is point symmetric?
(a) Equilateral triangle
(b) Trapezium
(c) Rectangle
(d) None of these

Answer 4:

A point of symmetry is a point that represents a "center" of sorts for the figure.
Hence, the correct answer is option (c)

Question 5:

The number of lines of symmetry of a square is
(a) 2
(b) 3
(c) 4
(d) Infinite

Answer 5:

The number of lines of symmetry of a square is 4.

Hence, the correct answer is option (c).

Question 6:

The number of lines of symmetry of a rectangle is
(a) 2
(b) 3
(c) 4
(d) 1

Answer 6:

The number of lines of symmetry of a rectangle is 2

Hence, the correct answer is option (a).

Question 7:

The number of lines of symmetry of an equilateral triangle is
(a) 1
(b) 2
(c) 3
(d) 0

Answer 7:

The number of lines of symmetry of an equilateral triangle is 3

Hence, the correct answer is option (c).

Question 8:

The order of rotational symmetry of an equilateral triangle is
(a) 0
(b) 1
(c) 2
(d) 3

Answer 8:

The order of rotational symmetry of an equilateral triangle is 3 i.e., 120°, 240° and 360°.
Hence, the correct answer is option (d).

Question 9:

A rectangle has rotational symmetry of order
(a) 1
(b) 2
(c) 3
(d) 4

Answer 9:

A rectangle has order of rotational symmetry of 2 i.e., 180° and 360°
Hence, the correct answer is option (b).

Question 10:

The number of lines of symmetry of an isosceles triangle is
(a) 0
(b) 1
(c) 2
(d) 3

Answer 10:

The number of lines of symmetry of an isosceles triangle is 1

Hence, the correct answer is option (b).

No comments:

Post a Comment

Home

Contact Form

Name

Email *

Message *