Page 218 - Start Up Mathematics_7

On the other hand, there are numerous objects which do not possess linear symmetry. Some of
them are given below.

Parallelogram Letter N Hand Cup

• A line of symmetry is also known as axis of symmetry.
• The concept of line symmetry is closely related to that of mirror reflection. A mirror line,
thus acts like a line of symmetry. The two parts on either side of a line of symmetry
are like mirror images of each other and hence one can observe left-right changes in
the orientation.

A Line Segment
A line segment has two lines of symmetry, i.e., the
line lying on the segment and the perpendicular A B
bisector of the segment.

A Line
A line has infinite lines of symmetry. Since
a line has infinite length, therefore, each line A B
per pendicular to the given line divides it into
two symmetrical parts. Besides this, a line is also
symmetrical to itself.

B
An Angle

An angle having equal arms has only one line of
symmetry, i.e., the internal bisector of the angle.
O
A
A
An Isosceles Triangle
An isosceles triangle is symmetrical about the
bisector of the angle included between the equal
sides which incidently is also its median.

B C
A Rectangle D C
A rectangle has two lines of symmetry, one
vertical and the other horizontal, each joining the
midpoints of the opposite sides.

A B

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