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SAI International School
CLASS – VII

SUB: MATH
CHAPTER-14:SYMMETRY

TOPIC: CONCEPTS OF SYMMETRY

SUBTOPIC: Line of symmetry, Reflection and symmetry,Mirror Reflection

LESSON NOTES:1

 Symmetry is when two or more parts are identical after a flip, slide or turn. It is
an important concept which is used in every field of activity.

Line of Symmetry:The line of symmetry can be defined as the axis or imaginary line
that passes through the center of the shape or object and divides it into identical
halves.

 Figures or shapes that have exact resemblance to its other part, when divided
into two or more equal parts are called symmetrical.

Ex-

Line of Symmetry for a regular polygon:A polygon is a closed figure made of
several line segments. The polygon made up of the least number of line segments is
the triangle.

 A polygon is said to be regular if all its sides are of equal length and all its
angles are of equal measure. Thus, an equilateral triangle is a regular polygon
of three sides.
 An equilateral triangle is regular because each of its sides has same length
and each of its angles measures 60°.
 A square is also regular because all its sides are of equal length and each of
its angles is a right angle (i.e., 90°). Its diagonals are seen to be perpendicular
bisectors of one another.
 Pentagon is regular; naturally, its sides should have equal length. You will,
later on, learn that the measure of each of its angles is 108°.
 A regular hexagon has all its sides equal and each of its angles measures
120°.