Ex 14.3, 4 Fill in the blanks: (Done before) Square
(Done before) Rectangle
Rhombus
If rotated by 90°
This figure is not same as initial figure
If rotated by 180°
This figure looks same as initial figure
Again rotated by 180°
Thus, in 1 full – turn (i.e 360°)
The figure is same as that of initial 2 turns
So, we say that this figure has rotational symmetry of order 2
Regular Hexagon
If rotated by 60°
Again rotate it by 60°
Here,
Angle at center = (360°)/6
= 60°
Thus,
Circle
If it rotates 180°
It looks same as initial figure
If it rotates 90°
It looks same as initial figure
If it rotates 45°
It looks same as initial figure
If it rotates 10°
It looks same as initial figure
If it rotates 0.1°
It looks same as initial figure
If it rotates 0.01°
It looks same as initial figure
Therefore,
Circle has infinite order of rotational symmetry
Semi-Circle
If it rotates 90°
It is not same as initial figure
If it rotates by 180°
This is not same as initial figure
If it rotates by 360°
This is same as initial figure
So, this figure on rotation is same as initial figure only when it has rotated 360°
So, it has order of rotational symmetry 1

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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