JEE Main & Advanced JEE Main Solved Paper-2014

  • question_answer
    If x = −1 and x = 2 are extreme points of \[f(x)=\alpha log|x|+\beta {{x}^{2}}+x\]then :   JEE Main  Solved  Paper-2014

    A) \[\alpha =-6,\beta =\frac{1}{2}\]              

    B) \[\alpha =-6,\beta =-\frac{1}{2}\]

    C) \[\alpha =2,\beta =-\frac{1}{2}\]              

    D) \[\alpha =2,\beta =\frac{1}{2}\]

    Correct Answer: C

    Solution :

    Here \[f'(x)=\frac{\alpha }{x}+2\beta x+1;\]\[f'(-1)=0\]is an extreme point)\[-\alpha -2\beta +1=0\]                       ?(1) Also, f′ (2) = 0 gives\[\frac{\alpha }{2}+4\beta +1=0\]?(2) Solving (1) and (2) gives \[\alpha =2,\beta =-\frac{1}{2}\]


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