JEE Main & Advanced JEE Main Paper (Held On 11 April 2015)

  • question_answer
    If the two roots of the equation, \[(a-1)({{x}^{4}}+{{x}^{2}}+1)+(a+1){{({{x}^{2}}+x+1)}^{2}}=0\]are real and distinct, then the set of all values of 'a' is: [JEE Main Online Paper (Held On 11 April 2015)]  

    A) \[\left( -\frac{1}{2},0 \right)\]

    B) \[(-\infty ,-2)\cup (2,\infty )\]

    C) \[\left( -\frac{1}{2},0 \right)\cup \left( 0,\frac{1}{2} \right)\]

    D) \[\left( 0,\frac{1}{2} \right)\]

    Correct Answer: C

    Solution :

      \[(a-1)\left( {{x}^{2}}+x+1 \right)\left( {{x}^{2}}-x+1 \right)+(a+1){{\left( {{x}^{2}}+x+1 \right)}^{2}}=0\] \[\Rightarrow \]\[{{x}^{2}}+x+1\]or\[(a-1)\left( {{x}^{2}}-x+1 \right)+(a+1)\left( {{x}^{2}}+x+1 \right)=0\] \[\Rightarrow \]\[a{{x}^{2}}+x+a=0\] For real & unequal roots D > 0 \[\Rightarrow \]\[1-4{{a}^{2}}>0\] \[\Rightarrow \]\[a\in \left( -\frac{1}{2},\frac{1}{2} \right)-\left\{ 0 \right\}\]\[\because \]\[a\ne 0\]


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