Question

(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?
[4 MARKS]

Answer 1

(a) Answer: 1 Mark
Example along with diagram: 1 Mark
(b) Definition: 1 Mark
(c) Answer: 1 Mark

(a) If it happens for ${120}^{\circ }$, it will also happen for multiples of ${120}^{\circ }$, such as ${240}^{\circ }$ and ${360}^{\circ }$.

The example is an equilateral triangle.



(b) The number of position in which the object looks exactly the same is called the order of rotational symmetry.

(c) The order of rotational symmetry of a semicircle is $1$.