Symmetry
- A figure has a line symmetry if a line can be drawn dividing the figure into two identical parts. The line is called a line of symmetry.
- A line segment is symmetrical at its perpendicular bisector.
- A figure may have no line of symmetry, only one line of symmetry, two lines of symmetry or multiple lines of symmetry.
Figure
|
Number of lines of symmetry
|
Angle
|
1
|
Scalene triangle
|
0
|
Isosceles triangle
|
1
|
Equilateral triangle
|
3
|
Parallelogram
|
0
|
Rhombus
|
2
|
Isosceles trapezium
|
1
|
Circle
|
Infinitely Many
|
Semicircle
|
1
|
Regular pentagon
|
5
|
Regular hexagon
|
6
|
- A line symmetry is closely related to mirror reflection. When dealing with mirror reflection, we have to take into account the left right changes in orientation.
- A figure may have a vertical or a horizontal line of symmetry.
- Of the digits 0 to 9, only 1, 3 and 8 have a horizontal line of symmetry, 8 has vertical line of symmetry also.
- Alphabets of English, A to...... Z have different lines of symmetry.
(i) The letter of the English alphabet with no line symmetry are F, G, J, L, N, P, Q, R, S and Z.
(ii) The letters A, M, T, U, V, W and Y have only vertical line of symmetry.
(iii) The letters B, C, D, E, and K have only horizontal line of symmetry.
(iv) The letters H, I and X have both vertical and horizontal lines of symmetry.