JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Condition for common roots, Quadratic expressions and Position of roots

  • question_answer
    If x is real, the expression  \[\frac{x+2}{2{{x}^{2}}+3x+6}\] takes all value in the interval [IIT 1969]

    A) \[\left( \frac{1}{13},\frac{1}{3} \right)\]

    B) \[\left[ -\frac{1}{13},\frac{1}{3} \right]\]

    C) \[\left( -\frac{1}{3},\frac{1}{13} \right)\]

    D) None of these

    Correct Answer: B

    Solution :

    If the given expression be y, then \[y=2{{x}^{2}}y+(3y-1)x+(6y-2)=0\] If \[y\ne 0\]then \[\Delta \ge 0\]for real x i.e. \[{{B}^{2}}-4AC\ge 0\] or - \[39{{y}^{2}}+10y+1\ge 0\]  or \[(13y+1)(3y-1)\le 0\] Þ \[-1/13\le y\le 1/3\] If \[y=0\] then \[x=-2\] which is real and this value of \[y\] is included in the above range.


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