JEE Main & Advanced Mathematics Functions Question Bank Functions

  • question_answer
    If x is real, then value of the expression \[\frac{{{x}^{2}}+14x+9}{{{x}^{2}}+2x+3}\] lies between [UPSEAT 2002]

    A)                    5 and 4

    B)            5 and ?4

    C)            ? 5 and 4

    D)            None of these

    Correct Answer: C

    Solution :

               \[\frac{{{x}^{2}}+14x+9}{{{x}^{2}}+2x+3}=y\] Þ \[{{x}^{2}}+14x+9={{x}^{2}}y+2xy+3y\]            Þ \[{{x}^{2}}(y-1)+2x(y-7)+(3y-9)=0\]            Since x is real,   \\[4{{(y-7)}^{2}}-4(3y-9)(y-1)>0\]            Þ \[4({{y}^{2}}+49-14y)-4(3{{y}^{2}}+9-12y)>0\]            Þ \[4{{y}^{2}}+196-56y-12{{y}^{2}}-36+48y>0\]            Þ \[8{{y}^{2}}+8y-160<0\] Þ \[{{y}^{2}}+y-20<0\]            Þ  \[(y+5)(y-4)<0\];   \ y lies between ? 5 and 4.


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