JEE Main & Advanced AIEEE Solved Paper-2010

  • question_answer
    Consider the following relations \[R=\{(x,y)|x,y\]are real numbers and\[x=wy\]for some rational number w}; \[S=\left\{ \left( \frac{m}{n},\frac{p}{q} \right) \right\}=|m,n,p\]and q are integers such that\[n,q\ne 0\]and\[qm=pn\}\]. Then -

    A) R is an equivalence relation but S is not an equivalence relation

    B) Neither R nor S is an equivalence relation

    C) S is an equivalence relation but R is not an equivalence relation

    D) R and S both are equivalence relations

    Correct Answer: C

    Solution :

    Probable part of R is {(0, 1), (0, 2)} But \[(1,\text{ }0)\notin R\] as \[1=(w)\text{ }0\] So not symmetric ie. not equivalence Relation \[\frac{m}{n}S\frac{p}{q}\to qm=pn\] Reflexive \[\frac{m}{n}S\frac{p}{q}\to mm=mn\] hence function reflexive . Let \[\frac{m}{n}S\frac{p}{q}\to qm=pn\] Then \[\frac{p}{q}S\frac{m}{n}\to qn=mq\] hence function symmetric \[\frac{m}{s}S\frac{p}{q}\to mq=pn\]                    (1) \[\frac{p}{q}S\frac{r}{s}\to ps=qr\]                          (2) eqn. (1)/(2) \[\frac{m}{n}=\frac{r}{s}\to \frac{m}{n}S\frac{r}{s}\] hence transitive So S is equivalence relation


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