Ex 12.2

Chapter 12 Class 7 Symmetry
Serial order wise

Transcript

Ex 12.2, 1 (a) Which of the following figures have rotational symmetry of order more than 1: Let’s rotate it by 90° Again rotate it by 90° Suppose it rotate by 90° again Once more, it rotates by 90° Thus, in 1 full turn (i.e. 360°) The figure is same as that of initial 4 turns. So, we say that figure has rotational symmetry of order 4 Ex 12.2, 1 (b) Which of the following figures have rotational symmetry of order more than 1: Let’s rotate it by 120° This figure looks same as previous. Again, rotate it by 120° This figure looks same as previous Suppose, it rotates by 120° again This figure looks same as previous Thus, in 1 full turn (i.e. 360°) This figure is same as that of initial 3 turns So, we say that figure has rotational symmetry of order 3 Ex 12.2, 1 (c) Which of the following figures have rotational symmetry of order more than 1: Let’s rotate it by 180° This does not looks like previous figure Again rotating by 180° This looks like initial figure. So, this figure on rotational is same as initial figure only when it has rotated 360° So, it has the order of rotational symmetry 1 Ex 12.2, 1 (d) Which of the following figures have rotational symmetry of order more than 1: Let’s rotate it by 180° This figure looks same as previous Again, rotate it by 180° This figure looks same as previous Thus, Thus, in 1 full turn (i.e 360° ) This figure is same as that of initial 2 turns So, we say that figure has rotational symmetry of order 2 Ex 12.2, 1 (e) Which of the following figures have rotational symmetry of order more than 1: Since circle is divided into 3 equal sectors, Angle at center = (360°)/3 = 120° This figure looks same as previous Suppose it rotates 120° again This figure looks same as previous Again it rotates 120° This figure looks same as previous Ex 12.2, 1 (f) Which of the following figures have rotational symmetry of order more than 1: Let’s rotate it by 90° This figure looks same as previous. Again rotating it by 90° This figure looks same as previous. Again it rotates it by 90° This figure looks same as previous. Suppose it again rotates 90° This figure looks same as previous. Thus, in 1 full-turn (i.e. 360°) The figure is same as that of initial 4 turns So, we say that figure has rotational symmetry of order 4 Hence, figure (a), (b), (d), (e) and (f) have rotational symmetry of order more than one

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.