Page 209 - ICSE Math 8

19 Symmetry, Reflection

and Rotation

Key Concepts

• Symmetry • Rotation
• Reflection • Rotational Symmetry

Symmetry

Take a white sheet of paper. Fold it as shown and then unfold it. Put a few drops of water
colour on the line of fold and fold it again. Keep the sheet pressed for sometime and then
open it. You will get a figure which is exactly the same on both sides of the line of fold.
Such a figure is called symmetric figure and the line of fold is called the line of symmetry.
A geometrical figure or an object is said to be symmetric if its one half is of exactly the
same size and shape as the other half. Given below are some geometrical figures with their
line(s) of symmetry.

Figure Lines of symmetry Symmetrical about Diagram

Perpendicular bisector
(a) Line segment 2
and the line itself A B

P

(b) Angle 1 Its bisector

Q R

P
Angle bisector of the
(c) Isosceles triangle 1 angle formed by equal
sides
Q R

P
Angle bisectors of 3
(d) Equilateral triangle 3
vertices
Q R

S R
Perpendicular bisectors
(e) Rectangle 2
of two adjacent sides
P Q

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