source: ncert
topic: geometry
class_level: class_7
chapter: ch14
difficulty: beginner
Class 7 | Ch14: Symmetry Line symmetry: one half is mirror image. Regular n-sided polygon: n lines of symmetry. Lines of symmetry: Equilateral triangle=3, Square=4, Rectangle=2(midpoints only), Rhombus=2(diagonals), Isosceles=1, Scalene=0, Kite=1, Parallelogram=0, Pentagon=5, Hexagon=6, Circle=infinite. Rotational symmetry: looks same after rotation<360°. Order=number of times in full rotation. Angle=360°÷order. Rotational: Square(order 4, angle 90°), Rectangle(order 2, 180°), Equilateral triangle(order 3, 120°), Hexagon(order 6, 60°), Parallelogram(order 2, 180°), Scalene(order 1=none). Square has BOTH line and rotational symmetry. Parallelogram: NO line symmetry but HAS rotational (order 2). Rectangle: 2 lines symmetry, order 2 rotation. Pentagon: order 5, angle 72°.