CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2006

  • question_answer
    Let\[{{x}_{1}}\]and\[{{x}_{2}}\]be solutions of the equation\[{{\sin }^{-1}}\left( {{x}^{2}}-3x+\frac{5}{2} \right)=\frac{\pi }{6}\].Then, the value of \[x_{1}^{2}+x_{2}^{2}\]is:

    A)  4                            

    B)         5

    C)  \[\frac{5}{2}\]                  

    D)         6

    E)  \[\frac{15}{2}\]

    Correct Answer: A

    Solution :

    \[{{\sin }^{-1}}\left( {{x}^{2}}-3x+\frac{5}{2} \right)=\frac{\pi }{6}\] \[\Rightarrow \]               \[{{x}^{2}}-3x+\frac{5}{2}=\sin \left( \frac{\pi }{6} \right)=\frac{1}{2}\] \[\Rightarrow \]               \[2{{x}^{2}}-6x+5=0\] Since,\[{{x}_{1}}\,{{x}_{2}}\], are the solution set, then \[{{x}_{1}}+\,{{x}_{2}}=\frac{6}{2}=3\] and            \[{{x}_{1}}\,{{x}_{2}}=\frac{5}{2}\] \[\therefore \]\[x_{1}^{2}+x_{2}^{2}={{({{x}_{1}}+{{x}_{2}})}^{2}}-2{{x}_{1}}{{x}_{2}}=9-5=4\]


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