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RAJASTHAN ­ PET Rajasthan PET Solved Paper-2006

  • question_answer
    If \[^{{{a}^{2}}-a}{{C}_{2}}{{=}^{{{a}^{2}}-a}}{{C}_{4}},\] then the value of q is

    A)  2                   

    B)  3

    C)  4                   

    D)  7

    Correct Answer: B

    Solution :

     Given, \[^{{{a}^{2}}-a}{{C}_{2}}{{=}^{{{a}^{2}}-a}}{{C}_{4}}\] \[\Rightarrow \] \[^{{{a}^{2}}-a}{{C}_{2}}{{=}^{{{a}^{2}}-a}}{{C}_{{{a}^{2}}-a-4}}\]\[[{{\because }^{n}}{{C}_{r}}{{=}^{n}}{{C}_{n-r}}]\] \[\Rightarrow \] \[{{a}^{2}}-a-4=2\] \[\Rightarrow \] \[{{a}^{2}}-a-6=0\] \[\Rightarrow \] \[(a-3)(a+2)=0\] \[\Rightarrow \] \[a=3\]or \[-2\]


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