JEE Main & Advanced JEE Main Paper (Held on 08-4-2019 Afternoon)

  • question_answer
    Let \[f:R\to R\]be a differentiable function satisfying\[f'(3)+f'(2)=0\] Then\[\underset{x\to 0}{\mathop{\lim }}\,{{\left( \frac{1+f(3+x)-f(3)}{1+f(2-x)-f(2)} \right)}^{\frac{1}{x}}}\]is equal to                                      [JEE Main 8-4-2019 Afternoon]

    A) \[{{e}^{2}}\]                                   

    B) \[e\]

    C) \[{{e}^{-1}}\]                      

    D)   1

    Correct Answer: D

    Solution :

    \[\underset{x\to 0}{\mathop{\lim }}\,{{\left( \frac{1+f(3+x)-f(3)}{1+f(2-x)-f(2)} \right)}^{\frac{1}{x}}}({{1}^{\infty }}form)\] \[\Rightarrow {{e}^{\underset{x\to 0}{\mathop{\lim }}\,\frac{f(3+x)-f(2-x)-f(3)+f(2)}{x(1+f(2-x)-f(2))}}}\] using L'Hopital \[\Rightarrow {{e}^{\underset{x\to 0}{\mathop{\lim }}\,\frac{f'(3+x)+f'(2-x)}{-xf'(2-x)+(1+f(2-x)-f(2))}}}\] \[\Rightarrow {{e}^{\frac{f'(3)+f'(2)}{1}}}=1\]


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