Page 208 - ICSE Math 7

7. A point A(5, 4) is reflected in x-axis to point B. Point B is further reflected in y-axis to point C.
Find the coordinates of B and C.
8. A point P(–3, –2) is reflected in origin to point Q and point Q is further reflected in x-axis to
point R. Find the coordinates of Q and R.
9. Which of the following shapes have rotational symmetry about the marked point (•). Also find
their order of rotational symmetry.

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

(e) (f) (g) (h)

AT A GLANCE

¾ A figure has line symmetry, if it can be folded along a line so that its two halves coincide.
¾ The two parts on either sides of line of symmetry are like mirror images of each other.
¾ Reflection of a point (x, y) in x-axis is (x, –y).
¾ Reflection of a point (x, y) in y-axis is (–x, y).

¾ Reflection of a point (x, y) in origin is (–x, –y).
¾ Rotation is a transformation which rotates all the points in a plane about a fixed point through
a given angle.

¾ The fixed point about which a figure is rotated is known as the centre of rotation.
¾ The minimum angle through which a figure is rotated to look exactly the same is called the angle
of rotation.
¾ The number of times a figure looks exactly the same in a complete turn (rotation of 360°) is
called the order of rotational symmetry.
360°
Order of rotational symmetry =
angle of rotation

MENTAL MATHS

1. Choose the correct answer.
(a) Which of the following have four lines of symmetry?
(i) parallelogram (ii) rhombus (iii) rectangle (iv) square
(b) What is the order of rotational symmetry of a figure which does not have rotational symmetry?
(i) 0 (ii) 1 (iii) 2 (iv) not defined
(c) A figure having 1 line of symmetry and whose order of rotational symmetry is also 1 is
__________.
(i) parallelogram (ii) rhombus (iii) semicircle (iv) a scalene triangle
(d) What is the order of rotation of a line segment?

(i) 4 (ii) 3 (iii) 1 (iv) 2

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