JEE Main & Advanced Sample Paper JEE Main Sample Paper-17

  • question_answer
    If the function \[f(x)=\frac{3{{x}^{2}}+ax+a+3}{{{x}^{2}}+x-2}\]is continuous at \[x=-2,\]then the value of\[f(-2)\] is

    A)  0                                            

    B) \[-1\]

    C)  1                                            

    D)  2

    Correct Answer: B

    Solution :

     Since the function is continuous at \[x=-2,\]then \[f(-2)=\underset{x\to -2}{\mathop{\lim }}\,f(x)\] \[=\underset{x\to -2}{\mathop{\lim }}\,\frac{3{{x}^{2}}+ax+a+3}{{{x}^{2}}+x-2}\] This limit will exist when \[15-a=0\] or            \[a=15.\]                                              ?(i) \[\therefore \]  \[f(-2)=\underset{x\to -2}{\mathop{\lim }}\,\frac{3{{x}^{2}}+15x+18}{{{x}^{2}}+x-2}\] \[=\underset{x\to -2}{\mathop{\lim }}\,\frac{3(x+2)(x+3)}{(x+2)(x-1)}\] \[=\underset{x\to -2}{\mathop{\lim }}\,\frac{3(x+3)}{(x-1)}\] \[=\frac{3}{-3}=-1\]


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