Page 202 - ICSE Math 7

Example 2: Choose the correct line(s) of symmetry for the following figures.
m
l
m n
(a) (b) (c) m
l l

Solution: (a) The figure is symmetrical about line l and not about line m.
(b) The figure is symmetrical about line m and not about lines l and n.
(c) The figure is symmetrical about both lines l and m.

EXERCISE 18.1

1. Draw the line(s) of symmetry for each figure, if possible.

(a) (b) (c) (d)

2. How many line(s) of symmetry do the following have?
(a) An equilateral triangle with each side of length 6 cm
(b) A semicircle with diameter 7.5 cm

(c) A circle with radius 2 cm
(d) A scalene triangle
(e) A quadrant of a circle with radius 4 cm

3. Name any three English letters which have a vertical line of symmetry and three which have a
horizontal line of symmetry.
4. If possible, draw a triangle with:
(a) zero line of symmetry (b) one line of symmetry
(c) two lines of symmetry (d) three lines of symmetry
5. Construct a triangle with AB = 3 cm, BC = 5 cm and CA = 6.5 cm. How many line(s) of symmetry
are possible in this triangle?
6. Construct a triangle PQR with PQ = QR = RP = 4 cm. How many line(s) of symmetry are possible
in this triangle?

7. Which quadrilateral has exactly two lines of symmetry?
8. Which quadrilateral need not have a line of symmetry?

Reflection
l
If any object is placed at some distance in front of a plane mirror,
then its image is formed at the same distance behind the mirror. In the
adjoining figure, if an object is placed at A, then its image is formed at
A'. The line segment joining A and A' is perpendicularly bisected by the A
A'
mirror line l. The mirror line is also known as the line of reflection. (Object) (Image)
If point A is situated on line l, then its image will coincide with it and
the point will be known as invariant point. Plane mirror

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