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SAI INTERNATIONAL SCHOOL
CBSE CURRICULUM
Class: VI Lesson Note 9.3
SUBJECT: Mathematics
CH: 9 -Symmetry
Sub Topic: Rotational Symmetry
→ Sometimes a figure looks the same when it is rotated by an angle about a fixed point. This fixed
point is called the centre of rotation. Such a figure is said to have rotational symmetry.
→ The angle by which the figure is rotated is called the angle of rotational symmetry or just the
angle of symmetry. This angle lies between 0 and 360 degrees.
→ A figure may have multiple angles of symmetry.
→ Smallest angle of symmetry = 360 ÷ (number of lines of symmetry in the figure)
→ Other angles are multiples of the smallest angle till we reach 360°.
→ Also, number of angles of symmetry = number of lines of symmetry.
→ The number of angles of symmetry is also called the order of rotational symmetry.
→ Minimum order of rotation symmetry is 1 as any object will look like itself after a complete turn.
The paper windmill in the picture looks symmetrical but there is no line of symmetry! However, you
fold it, the two halves will not exactly overlap. On the other hand, if you rotate it by 90° about the
red point at the centre, the windmill looks the same. We say that the windmill has rotational
symmetry.
When talking of rotational symmetry, there is always a fixed point about which the object is rotated.
