Q87 / 180 · KCET 2010 · Mathematics

In $P(X)$, the power set of a non-empty set $X$, an binary operation * is defined by $\mathrm{A}{ }^{*} \mathrm{~B}=\mathrm{A} \cup \mathrm{B}, \forall \mathrm{A}, \mathrm{B} \in \mathrm{P}(\mathrm{x})$ under $*$, a true statement is

  • A
    identity law is not satisfied
  • Correct answer
    B
    inverse law is not satisfied
  • C
    commutative law is not satisfied
  • D
    associative law is not satisfied

Solution

Under the binary operation, $\mathrm{A} * \mathrm{~B}=\mathrm{A} \cup \mathrm{B}, \forall \mathrm{A}, \mathrm{B} \in \mathrm{P}(\mathrm{x})=$ Power set Inverse of 'A' does not exists because $$ A * B \neq \phi \text {, for any } B \in P(x) $$ Where $\phi$ is the identity element in $P(x)$. While under the binary operation $A * B=A \cup B$, the commutative law, associative law and identity elements are exists.

Hence, the correct answer is option: 'B'.

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