Question 10
Find the angles of symmetry for the given figures about the point marked •.
(a) (b) (c)
We need to find the smallest angle to turn each figure so it looks exactly the same. This is called the angle of symmetry.
Step 1 — Figure (a)
Let us look at figure (a). It is a cross shape. The marked point • is at its center. Imagine rotating this figure around the center point. If we turn it by 90°, the figure will look exactly the same. It will look the same 4 times in a full circle. A full circle is 360°. So, we divide 360° by the number of times it looks the same.
Step 2 — Figure (b)
Let us look at figure (b). It is a vertical line with two small squares. The squares are at the ends. They point outwards. The marked point • is at the center of the line. Imagine rotating this figure around the center point. If we turn it by 90°, it will not look the same. If we turn it by 180°, the squares will point inwards. It will not look the same. The figure only looks the same after a full turn. This means it looks the same 1 time in a full circle. A full circle is 360°.
Step 3 — Figure (c)
Let us look at figure (c). It looks like the letter 'H'. It has two vertical lines. A horizontal line connects them. The marked point • is at the center of the horizontal line. Imagine rotating this figure around the center point. If we turn it by 90°, it will not look the same. If we turn it by 180°, it will look exactly the same. It will look the same 2 times in a full circle. A full circle is 360°.
Answer
(a) 90° (b) 360° (c) 180°
More questions in FIO
Do you see any line of symmetry in the figures at the start of the chapter? What about in the picture of the cloud?
For each of the following figures, identify the line(s) of symmetry if it exists.
Punching Game
The fold is a line of symmetry. Punch holes at different locations of a folded square sheet of paper using a punching machine and create different symmetric patterns.
In each of the following figures, a hole was punched in a folded square sheet of paper and then the paper was unfolded. Identify the line along which the paper was folded. Figure (d) was created by punching a single hole. How was the paper folded?
Given the line(s) of symmetry, find the other hole(s):
Here are some questions on paper cutting. Consider a vertical fold. We represent it this way:
Vertical Fold
Similarly, a horizontal fold is represented as follows:
Horizontal Fold
After each of the following cuts, predict the shape of the hole when the paper is opened. After you have made your prediction, make the cutouts and verify your answer.
Trace each figure and draw the lines of symmetry, if any:
Copy the following on a dot grid. For each figure draw two more lines to make a shape that has a line of symmetry.
Find the angles of symmetry for the given figures about the point marked •.
(a) (b) (c)
Which of the following figures have more than one angle of symmetry?
Give the order of rotational symmetry for each figure:
Colour the sectors of the circle below so that the figure has:
(i) 3 angles of symmetry
(ii) 4 angles of symmetry
(iii) What are the possible numbers of angles of symmetry you can obtain by colouring the sectors in different ways?
Draw two figures other than a circle and a square that have both reflection symmetry and rotational symmetry.
Draw, wherever possible, a rough sketch of:
a. A triangle with at least two lines of symmetry and at least two angles of symmetry.
b. A triangle with only one line of symmetry but not having rotational symmetry.
c. A quadrilateral with rotational symmetry but no reflection symmetry.
d. A quadrilateral with reflection symmetry but not having rotational symmetry.
In a figure, 60° is the smallest angle of symmetry. What are the other angles of symmetry of this figure?
In a figure, 60° is an angle of symmetry. The figure has two angles of symmetry less than 60°. What is its smallest angle of symmetry?
Can we have a figure with rotational symmetry whose smallest angle of symmetry is:
a. 45°?
b. 17°?