KVPY Sample Paper KVPY Stream-SX Model Paper-16

  • question_answer
    If \[\underset{x\to 0}{\mathop{Lim}}\,\,\,\frac{{{729}^{x}}-{{243}^{x}}-{{81}^{x}}+{{9}^{x}}+{{3}^{x}}-1}{{{x}^{3}}}=K{{(\ell n3)}^{3}}\] then K is equal to -

    A) 4

    B) 5    

    C) 6

    D) 8

    Correct Answer: C

    Solution :

    \[\underset{x\to 0}{\mathop{Lim}}\,\frac{{{3}^{6x}}-{{3}^{5x}}-{{3}^{4x}}+{{3}^{2x}}+{{3}^{x}}-1}{{{x}^{3}}}\]
    =\[\underset{x\to 0}{\mathop{Lim}}\,\frac{({{3}^{x}}-1)({{3}^{5x}}-{{3}^{3x}}-{{3}^{2x}}+1)}{{{x}^{3}}}\]
    =\[\underset{x\to 0}{\mathop{Lim}}\,\frac{({{3}^{x}}-1)({{3}^{2x}}-1)({{3}^{3x}}-1)}{{{x}^{3}}}\]
    =\[(\ell n3)\,\,(2\ell n3)\,\,(3\ell n3)=\,6{{(\ell n3)}^{3}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner