JEE Main & Advanced JEE Main Paper (Held On 10-Jan-2019 Evening)

  • question_answer
    The value of \[\lambda \]. such that sum of the squares of the roots of the quadratic equation, \[{{x}^{2}}+(3-\lambda )x+2=\lambda \] has the least value is- [JEE Main Online Paper (Held On 10-Jan-2019 Evening]

    A) 1                                 

    B) 2     

    C) \[\frac{15}{8}\]             

    D)                  \[\frac{4}{9}\]

    Correct Answer: B

    Solution :

    Sum of roots \[\alpha +\beta =-(3-\lambda )\] Product of roots \[\alpha \beta \,\,=\,\,2-\lambda \] \[{{\alpha }^{2}}+{{\beta }^{2}}={{\left( \alpha +\beta  \right)}^{2}}-2\alpha \beta \] \[=\,\,{{(3-\lambda )}^{2}}-2(2-\lambda )\] \[=\text{ }9+{{\lambda }^{2}}-6\lambda -4+2\lambda \] \[=\,\,{{\lambda }^{2}}-4\,\lambda +5\] \[{{\alpha }^{2}}+{{\beta }^{2}}\] is least then \[\lambda =-\frac{b}{2a}\] \[\lambda =-\frac{-(-4)}{2}\,\,=\,\,2\]


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