Page 212 - ICSE Math 6

20 Symmetry

Key Concepts

• Symmetry and line of Symmetry • To Construct a Line with Respect to which Two Given
• Reflection and Symmetry Points are Symmetric
• To Construct a Point Symmetric to a Given Point with
Respect to a Line

Symmetry

You must have noticed that there are two-dimensional objects and figures around us whose one half is
of exactly the same size and shape as the other half. Such objects or figures are known as symmetric
figures. The figures with two different halves are known as nonsymmetric figures.

Symmetric figures Nonsymmetric figures

Any figure which is symmetrical about a line passing through it is said to have linear symmetry.

Line of symmetry
A figure has line symmetry, if it can be divided by a line into two equal Maths Info
halves, each of which is the mirror image of the other. The line is called
the axis of symmetry or line of symmetry. If the figure is folded along A symmetrical figure can have
the line of symmetry, the two halves of the figure coincide. more than one line of symmetry.

1 line of symmetry 1 line of symmetry 2 lines of symmetry

Lines of symmetry of some geometrical figures
(a) A line segment is symmetrical about its perpendicular bisector
and the line itself. Thus, a line segment has 2 lines of symmetry. A B

A
(b) An angle is symmetrical about its bisector and hence has only
1 line of symmetry. O
B

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