Symmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection. The second meaning is a precise and well-defined concept of balance or "patterned self-similarity" that can be demonstrated or proved according to the rules of a formal system: by geometry, through physics or otherwise.
An equilateral triangle is regular because each of its sides has same lengths and each of its angles measure 60°. A square is also regular because all its sides are of equal lengths and each of its angle is a right angle (i.e.90 °). Its diagonals are seem to be perpendicular bisectors of one another.
If pentagon is regular, naturally, its sides should have equal length. Measure of each of its angle is 108°.A regular hexagon has all its sides equal and each of its anglesmeasures 120°.
LINES OF SYMMETRY Triangle Square Pentagon Hexagon3 lines of 4 lines of 5 lines of 6 lines ofSymmetry Symmetry Symmetry Symmetry
Points to remember Any object or shape is said to have rotational symmetry if it looks exactly the same at least once during a complete rotation through three hundred and sixty degrees. During the rotation, the object rotates around a fixed point. Its shape and size do not change. This fixed point is called the centre of rotation. Rotation may be clockwise or anti-clockwise. A full turn refers to a rotation of three hundred and sixty degrees. A half turn refers to a rotation of one hundred and eighty degrees. A quarter turn refers to a rotation of ninety degrees. The angle at which a shape or an object looks exactly the same during rotation is called the angle of rotation. The order of rotational symmetry can be defined as the number of times that a shape appears exactly the same during a full 360orotation.
ROTATIONAL SYMMETRYWhen an object rotates, its shapes and size do not change. The rotation turns an object about a fixed point. This fixed point is the centre of the rotation.The angle of turning during rotation is called angle of rotation. A full turn is 360o.
• Half turn means rotation by 180 °. A quarter turn is rotation by 90 °.
WHICH LETTERS HAVROTATIONAL SYMMETRY? Next slide for answer
WHICH ROAD SIGNS HAVE GOT ROTAIONAL SYMMETRY? • Next slide for answer…