JCECE Engineering JCECE Engineering Solved Paper-2004

  • question_answer
    If\[z=x+iy\]and\[\left| \frac{1-iz}{z-i} \right|=1\], the locus of\[z\]is:

    A)  \[x-\]axis

    B)  \[y-\]axis

    C)  circle with unity radius

    D)  none of the above

    Correct Answer: A

    Solution :

    We have\[\left| \frac{1-iz}{z-i} \right|=1\] \[\Rightarrow \]                          \[|1-iz|=|z-i|\] \[\Rightarrow \]               \[|1-i(x+iy)|=|x+iy-i|\] \[\Rightarrow \]                   \[|1-ix+y|=|x+i(y-1)|\] \[\Rightarrow \]        \[|{{(1+y)}^{2}}+{{x}^{2}}={{x}^{2}}+{{(y-1)}^{2}}\] \[\Rightarrow \]   \[1+{{y}^{2}}+2y+{{x}^{2}}={{x}^{2}}+{{y}^{2}}+1-2y\] \[\Rightarrow \]                               \[4y=0\] \[\Rightarrow \]                                  \[y=0\] \[\Rightarrow \]                               \[x-\]axis.


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