Definition of Order of Rotational Symmetry:

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

If A° is the smallest angle by which a figure is rotated so that rotated from fits onto the original form, then the order of rotational symmetry is given by \(\frac{360°}{A°}\), [A° < 180°]

Order of rotational symmetry = \(\frac{360}{\textrm{Angle of Rotation}}\)

A figure has a rotational symmetry of order 1, if it can come to its original position after full rotation or 360°.

Examples of Order of Rotational Symmetry:

Rectangle (clockwise)

We observe that while rotating the figure through 360°, it attains
original from two times i.e., it looks exactly the same at two positions. Thus,
we say that the rectangle has a rotational symmetry of order 2.

Equilateral triangle (clockwise):

We observe that at all 3 positions, the triangle looks exactly the same when rotated about its center by 120°.

Letter B (clockwise):

We observe that only at one position the letter looks exactly the same after taking one complete rotation.

Windmill (anticlockwise):

We observe that if we rotate it by one – quarter, at 4 positions, it looks exactly the same. Therefore, the order of rotational symmetry is 4.

Solved Examples on Order of Rotational Symmetry:

1. Find the order of rotational symmetry of the following shapes about the point marked.

Solution:

(i)

Order of rotational symmetry = \(\frac{360}{180}\) = 2

(ii)

Order of rotational symmetry = \(\frac{360}{60}\) = 6

2. The figure obtained by giving 2 anticlockwise right-angle turns to letter G is:

Answer: (ii)

● Related Concepts

● Reflection of a Point in x-axis

● Reflection of a Point in y-axis

● Reflection of a point in origin

● Rotation

● 90 Degree Clockwise Rotation

● 90 Degree Anticlockwise Rotation

7th Grade Math Problems

8th Grade Math Practice
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