JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Geometry of complex numbers

  • question_answer
    If \[z=x+iy\] and \[|z-zi|\,=1,\]then [RPET 1988, 91]

    A) \[z\]lies on \[x\]-axis

    B) \[z\]lies on \[y\]-axis

    C) z lies on a circle

    D) None of these

    Correct Answer: C

    Solution :

    Here \[|z-zi|=1\Rightarrow |x+iy-i(x+iy)|=1\] Þ \[|(x+y)+i(y-x)|=1\]Þ \[2{{x}^{2}}{{y}^{2}}=2{{x}^{2}}{{y}^{2}}+4{{x}^{2}}\] Þ \[2({{x}^{2}}+{{y}^{2}})=1\]. Hence z lies on a circle.


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