Important Concepts and Formulas
1. A figure is symmetrical about the
line which divides the figure into two identical parts.
2. The line which divides the figure
into two identical parts is called the line of symmetry or mirror line.
3. Regular polygons have as many lines
of symmetry as they have sides. For example, equilateral triangle–3, square–4,
pentagon–5 and hexagon–6, etc.
To see more figures with lines of symmetry ----- Click Here!
To see more figures with lines of symmetry ----- Click Here!
4. When half of a figure is the mirror
image of the other, it is said to have reflection symmetry.
5. Some of the capital letters of the
English alphabet are symmetrical such as A, B, C, D, E, H, I, M, O, T, U, V, W,
X.
6. Non-symmetrical shapes are called
asymmetrical shapes.
7. Rotational symmetry is the property
that an object has in which it looks the same after some rotation by a partial
turn. A complete turn is equal to 360°.
8. When an object rotates about a fixed
point, this fixed point is called the center of rotation.
9. An object having rotational symmetry
looks exactly the same after every rotation through a particular angle and that
angle is called the angle of rotation.
10. If x° is the angle of rotation of a
shape, then its order of rotational symmetry is 360° ÷ x°.
11. The smallest order of rotational
symmetry is 2. The order of rotational symmetry of objects that have no rotational
symmetry is considered as 1.