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Chapter 1 Class 12 Relation and Functions
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Ex 1.4, 8 - Let a * b = HCF of a and b. Is * commutative - Whether binary commutative/associative or not

Ex 1.4, 8 - Chapter 1 Class 12 Relation and Functions - Part 2
Ex 1.4, 8 - Chapter 1 Class 12 Relation and Functions - Part 3

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Ex 1.4, 8 Let * be the binary operation on N defined by a * b = H.C.F. of a and b. Is * commutative? Is *associative? Does there exist identity for this binary operation on N? Check commutative * is commutative if a * b = b * a Since a * b = b * a ∀ a, b ∈ N * is commutative Check associative * is associative if (a * b) * c = a * (b * c) Since (a * b) * c = a * (b * c) ∀ a, b ∈ N * is associative Identity Element e is the identity of * if a * e = e * a = a i.e. HCF of a & e = HCF of e & a = a There is no value of e which satisfies the given condition Example: Let e = 1 HCF of a & 1 = 1 ≠ a HCF of 1 & a = 1 ≠ a Thus, there is no identity of * in N.

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.