RD Sharma solution class 7 chapter 18 Symmetry Exercise 18.1

Exercise 18.1

Page-18.6

Question 1:

State the number of lines of symmetry for the following figures:
(i) An equilateral triangle
(ii) An isosceles triangle
(iii) A scalene triangle
(iv) A rectangle
(v) A rhombus
(vi) A square
(vii) A parallelogram
(viii) A quadrilateral
(ix) A regular pentagon
(x) A regular hexagon
(xi) A circle
(xii) A semicircle

Answer 1:

(i) An equilateral triangle has 3 lines of symmetry.
(ii) An isosceles triangle has 1 line of symmetry.
(iii) A scalene triangle has no line of symmetry.
(iv) A rectangle has 2 lines of symmetry.
(v) A rhombus has 2 lines of symmetry.
(vi) A square has 4 lines of symmetry.
(vii) A parallelogram has no line of symmetry.
(viii) A quadrilateral has no line of symmetry.
(ix) A regular pentagon has 5 lines of symmetry.
(x) A regular hexagon has 6 lines of symmetry.
(xi) A circle has an infinite number of lines of symmetry all along the diameters.
(xii) A semicircle has only one line of symmetry.

Page-18.7

Question 2:

What other name can you give to the line of symmetry of
(i) An isosceles triangle?
(ii) A circle?

Answer 2:

(i) An isosceles triangle has only 1 line of symmetry.
    
   This line of symmetry is also known as the altitude of an isosceles triangle.

(ii) A circle has an infinite number of lines of symmetry all along its diameters.
     

Question 3:

Identify three examples of shapes with no line of symmetry.

Answer 3:

A scalene triangle, a parallelogram and a trapezium do not have any line of symmetry.

Question 4:

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

Answer 4:

(A) The given figure has 3 lines of symmetry. Therefore it has multiple lines of symmetry.
     
(B) The given figure has 2 lines of symmetry. Therefore it has multiple lines of symmetry.
     
(C) The given figure has 3 lines of symmetry. Therefore it has multiple lines of symmetry.
     
(D) The given figure has 2 lines of symmetry. Therefore it has multiple lines of symmetry.
     
(E) The given figure has 4 lines of symmetry. Therefore it has multiple lines of symmetry.
     
(F) The given figure has only 1 line of symmetry.
    
(G) The given figure has 4 lines of symmetry. Therefore it has multiple lines of symmetry.
      
(H) The given figure has 6 lines of symmetry. Therefore it has multiple lines of symmetry.