Chapter 17- Symmetry completely focuses on the symmetric object and their number of lines of symmetry. The images or things that can be divided into two identical halves are known as symmetrical. On the contrary, asymmetrical objects are those which cannot be divided into two halves. It is easier to identify symmetrical objects in our daily lives. The other half should be exactly similar to the first half. The Line of symmetry is also an important concept to be followed in Chapter 17- Symmetry. A line that separates a figure, shape or solid into two halves is called the line of symmetry. It can also be defined as the imaginary line or axis along which an image is folded to obtain an asymmetrical shape. The shape can have more than one line of symmetry based on the shape. For example, the diagonal of a square divides it into two halves. The diagonal is known as the line of symmetry for the respective square.
Lines of symmetry always coincide with each other. There are different types of symmetry, namely translational symmetry, rotational symmetry, reflexive symmetry, and glide symmetry. The rules of symmetry should be followed when moved, rotated or flipped. When an object is translated and moved from one position to another, translation symmetry takes place. Rotational symmetry exists when an object is turned and is identical to its origin. Most of the shapes follow rotation symmetry in geometry.
A brief mention of both translation and reflection, also known as glide reflection, is mentioned in the latter part of the chapter. Finally, a small description of shapes is provided, stating that 'shapes can be regular or irregular. Furthermore, depending on nature, the shapes can have symmetry in different ways.