What is the order of rotation and centre of Rotation for Semi-circle?

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Solution

The centre of rotation of a semi-circle is the mid-point of the diameter.

Order of rotation of a semicircle is 1, because it looks the same as its initial position only once in four 90 degree turns .

As when we rotate it from 0° to 360° we get the exact image of semi-circle only once i.e., when it has been rotated at an angle of 360°. On other angles we will not get the exact image

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For a circle, the order of rotation is

Q. Question 4
Fill in the blanks:

\begin{matrix} S h a p e & C e n t r e o f R o t a t i o n & O r d e r o f R o t a t i o n & A n g l e o f R o t a t i o n S q u a r e R e c t a n g l e R h o m b u s E q u i l a t e r a l t r i a n g l e R e g u l a r h e x a g o n C i r c l e S e m i - c i r c l e \end{matrix}

Fill in the blanks:

Shape	Centre of Rotation	Order of Rotation	Angle of Rotation
Square	-	-	-
Rectangle	-	-	-
Rhombus	-	-	-
Equilateral Triangle	-	-	-
Regular Hexagon	-	-	-
Circle	-	-	-
Semi-circle	-	-	-

Q. How many center of rotation are in the square, rectangle,Rhombus circles and a semi circle

(a) After rotating through an angle of 120 degrees through its centre of symmetry the figure looks exactly the same as its original. At what other angles will it happen for the figure? Describe with an example.

(b) What is the order of rotational symmetry?

(c) What is the order of rotational symmetry of a semi-circle?
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