Symmetry

About this chapter

Symmetry is Chapter 9 of Class 6 Ganita Prakash. The chapter builds two big ideas — line (reflection) symmetry and rotational symmetry — through everyday Indian objects like rangoli, the Taj Mahal, a kolam, the Ashoka Chakra, a paper windmill and a bicycle wheel. A figure is symmetric when some part of it repeats in a definite pattern. A line of symmetry (or axis of symmetry) cuts the figure into two parts that exactly overlap on folding; one half is the reflection of the other. Figures may have zero, one or many lines of symmetry — a square has 4, an equilateral triangle has 3, a regular hexagon has 6 and a circle has infinitely many. A figure has rotational symmetry if it looks the same after a rotation by some angle (less than a full turn) about a fixed centre of rotation. The angles for which this happens are angles of symmetry; their count is the order. For n radial arms equally spaced, the smallest angle is 360 deg divided by n. CTET Paper 2 Maths tests this chapter through counting lines and angles of symmetry, identifying centre of rotation, recognising figures from punched-paper folds and applying these ideas to rangoli, kolam and national symbols. The four tests below check these ideas at the right depth.