RS Aggarwal Class 7 Math Eighteenth Chapter Reflection and Rotational Symmetry Exercise 18B Solution

RS Aggarwal Class 7 Math Eighteenth Chapter Reflection and Rotational Symmetry Exercise 18B Solution

EXERCISE 18B

(1) (i) How many lines of symmetry does an equilateral triangle have?

Ans: An equilateral triangle has lines of symmetry.

(ii) What is the order of rotational symmetry of an equilateral triangle?

Ans: The number of times a figure fits onto itself in one complete rotation is called the order of rotational symmetry.

So, the order  of rotational symmetry of an equilateral triangle is 3.

(2) Through what different angles should a rectangle be rotated to be in symmetrical position with the original position?

Ans: The rectangle rotate be 180^o or 360^o  it looked like symmetrical.

(3) What is the order of rotational symmetry of a square? Give the angles of such rotations.

Ans: The order of rotational symmetry of a square is 4.

If rotate the square by 90^o, 180^o, 270^o and 360^o, the square looks exactly the same.

(4) (i) How many lines of symmetry does a rhombus have?

Ans: A rhombus has 2 lines of symmetry.

(ii) What is the order of rotational symmetry of a rhombus?

Ans: The rotational symmetry of rhombus is 2. Because the rhombus rotate to 180^o and 360^o it looks like same.

(5) Write three letters of English alphabet which have two lines of symmetry and rotational symmetry of order 2.

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

Ans: An isosceles triangle has a line of symmetry but does not have rotational symmetry. Because the line of symmetry of an isosceles triangle is the angle bisector of its vertical angle, which is in between the equal sides.

(7) Does every trapezium have a line of symmetry?

Ans: No, every trapezium does not have a line of symmetry.

(8) What is the line of symmetry of semicircle? Does it have rotational symmetry?

Ans: The perpendicular bisector of the diameter of a circle is its line or symmetry.

No, a semicircle does not have any rotational symmetry as it fits itself only once during a complete rotation.

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

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

(10) Find (i) the number of lines of symmetry and

Ans: The line of symmetry of the given figure is 1.

(ii) The order of rotational symmetry of the adjoining figure. Draw the line of symmetry.

Ans: The order of rotational symmetry of the given figure is 0.

(11) (i) How many lines of symmetry does the given figure have? Draw

Ans: The given figure has 2 lines of symmetry.

(ii) What is the order of rotational symmetry of the given figure?

Ans: The order of rotational symmetry of the given figure is 2.

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

Ans: The example of a letter of the English alphabet system which has (i) no line of symmetry and (ii) rotational symmetry of order 2 is N.