Page 230 - Start Up Mathematics_7

At a Glance

1. A figure has line symmetry, if it can be folded along a line so that its two halves coincide.

2. The two parts on either sides of line of symmetry are like mirror images of each other.
3. A regular polygon has as many lines of symmetry as its sides. If its number of sides are odd,
the perpendicular bisector of its sides are the lines of symmetry. If the number of sides are
even, then besides the lines of symmetry as in an odd numbered regular polygon the lines
joining the opposite vertices are also the lines of symmetry.
4. Translation symmetry is the motion along a line in a specific direction by a specific distance.

5. Figures which on rotation of less than 360° about some point attains the same shape are said
to possess rotational symmetry.
6. The minimum angle through which a figure is rotated to look exactly the same is called the
angle of rotation.
7. 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 =

Review Exercises

Multiple ChoiCe Questions
1. A quadrilateral having four lines of symmetry is a:
(a) parallelogram (b) rhombus (c) rectangle (d) square
2. The order of rotational symmetry of a figure which does not have rotational symmetry is:
(a) 0 (b) 1 (c) 2 (d) not defined
3. A figure having 1 line of symmetry and whose order of rotational symmetry is also 1 is:
(a) parallelogram (b) rhombus (c) semicircle (d) a scalene triangle
4. The order of rotation of a line segment is:
(a) 4 (b) 3 (c) 1 (d) 2
5. Rotating a figure through 60° clockwise is equivalent to an anticlockwise rotation of:
(a) 60° (b) 120° (c) 300° (d) 360°
6. Number of lines of symmetry of a hexagon is:
(a) 4 (b) 5 (c) 6 (d) 0
7. A possible angle of rotation of a figure having rotational symmetry of order greater than 1 is:
(a) 26° (b) 72° (c) 200° (d) 360°
8. A paper pinwheel shown in the given figure has a rotational symmetry of order:
(a) 1 (b) 2 (c) 5 (d) 8
9. If a mirror is kept along the oblique line, the correct reflection is:

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

10. A quadrilateral cannot have the following lines of symmetry.
(a) 0 (b) 1 (c) 2 (d) 3

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