BCECE Engineering BCECE Engineering Solved Paper-2014

  • question_answer
          1f \[\left| z-\frac{4}{z} \right|=2\], then the maximum value of \[|z|\] is  equal to

    A) \[\sqrt{3}+1\]                   

    B) \[\sqrt{5}+1\]

    C) \[2\]                                     

    D) \[2+\sqrt{2}\]

    Correct Answer: B

    Solution :

    Now, \[|z|\left| \left( z-\frac{4}{z} \right)+\frac{4}{z} \right|\] \[\Rightarrow \]               \[|z|\le \left| z-\frac{4}{z} \right|+\left| \frac{4}{z} \right|\] \[\Rightarrow \]               \[|z|\le 2+\frac{4}{|z|}\]             \[\left( \because \left| z-\frac{4}{z} \right|=2 \right)\] \[\Rightarrow \]               \[\Rightarrow |z{{|}^{2}}-2|z|-4\le 0\] \[\Rightarrow \]               \[(|z|-(\sqrt{5+1}))(|z|-(1-\sqrt{5}))\le 0\] \[\Rightarrow \]               \[1-\sqrt{5}\le |z|\le \sqrt{5}+1\]


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