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

  • question_answer
    If \[|z+1|\,\,=\sqrt{2}|z-1|,\]then the locus described by the point \[z\] in the Argand diagram is a

    A) Straight line

    B) Circle

    C) Parabola

    D) None of these

    Correct Answer: B

    Solution :

    \[|z+1|=\sqrt{2}|z-1|\] Putting \[z=x+iy\] Þ \[|x+iy+1|=\sqrt{2}|x+iy-1|\] Þ \[|(x+1)+iy|=\sqrt{2}|(x-1)+iy|\] Þ \[{{(x+1)}^{2}}+{{y}^{2}}=2[{{(x-1)}^{2}}+{{y}^{2}}]\] Þ \[{{x}^{2}}+{{y}^{2}}-6x+1=0\]. Which is the equation of a circle.


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