Page 213 - ICSE Math 6

P
(c) An isosceles triangle is symmetrical about the angle bisector of
the angle formed by its equal sides. Thus, there is only 1 line
of symmetry.
Q R

A
(d) An equilateral triangle is symmetrical about the angle bisectors
of three angles. The angle bisectors are also the perpendicular
bisectors of its sides. Thus, there are 3 lines of symmetry.
B C

(e) A rectangle is symmetrical about the perpendicular bisectors of D C
two adjacent sides. Thus, there are 2 lines of symmetry.
A B
S R
(f) A square is symmetrical about the perpendicular bisectors of two
adjacent sides and the two diagonals. Thus, there are 4 lines of
symmetry.
P Q

(g) A circle is symmetrical about any line passing through its centre.
Thus, there are infinite lines of symmetry.
O

(h) A semicircle is symmetrical about the perpendicular bisector of
the diameter. Thus, there is only 1 line of symmetry.
A B

A
(i) An arc is symmetrical about the perpendicular bisector of
the line segment joining its end points. Thus, there is only
1 line of symmetry. B

(j) A segment is symmetrical about the perpendicular bisector P Q
of the chord that bounds the segment. Thus, there is only O
1 line of symmetry.

A
(k) A sector is symmetrical about the bisector of the angle formed
by the radii that bind the sector. Thus, there is only 1 line of O
symmetry. B

(l) An arrowhead has only 1 line of symmetry as shown in the
adjoining figure.

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