11th Class Mathematics Sample Paper Mathematics Olympiad - Sample Paper-7

  • question_answer
    \[x=\sqrt{-1-\sqrt{-1\sqrt{-1......}}}to\,\infty =\]

    A)  1                   

    B)  w              

    C)  \[-1\]                           

    D)  0

    Correct Answer: B

    Solution :

    [b] Let \[y=\sqrt{-1-\sqrt{1-}\sqrt{-1}}..........+\infty \] \[y=\sqrt{-1-y}\] \[{{y}^{2}}=-1-y\] \[\Rightarrow {{y}^{2}}+y+1=0\] \[\therefore y=\frac{-1\pm \sqrt{1-4.1.1}}{2.1}\] \[=\frac{-1\pm \sqrt{3}}{2}=\frac{-1\pm \sqrt{3i}}{2}=\omega \,or{{\omega }^{2}}\] Let \[y=\frac{-1+\sqrt{3i}}{2}=\omega \] then \[y=\frac{-1-\sqrt{3}}{2}={{\omega }^{2}}\] Hence option [b] is correct.


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