Page 219 - Start Up Mathematics_7

A Rhombus
S R
A rhombus is symmetrical about its diagonals.
Therefore, it has 2 lines of symmetry.

P Q

A Kite
D
A kite has only one line of symmetry. It is the diagonal
obtained by joining the vertices formed by intersection A C
of equal sides.

An Isosceles Trapezium B

In an isosceles trapezium, we have one pair of parallel
sides and the other pair of non-parallel equal sides. It D C
has only one line of symmetry, i.e., the line joining
the midpoints of the two parallel sides.

A B

A Semicircle
A semicircle has only one line of symmetry, i.e., the
perpendicular bisector of the diameter on which the
semicircle is drawn.
A O B
Lines of Symmetry of Some Regular Polygons
We know a polygon is a closed figure formed by line segments joining only at their end points.
The minimum line segments required to make a polygon is 3, i.e., a triangle. A polygon made up of
4, 5 and 6 sides is known as a quadrilateral, pentagon and hexagon, respectively. A polygon is
said to be regular if all its sides are equal and all its angles have the same measure. An equilateral
triangle and a square are regular polygons of 3 and 4 sides respectively. All regular polygons have
multiple lines of symmetry. In fact, each regular polygon has as many lines of symmetry as its
sides. Let’s verify it.

An equilateral triangle
An equilateral triangle has 3 lines of symmetry. Each
line of symmetry is a median of the triangle.

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