JEE Main & Advanced AIEEE Solved Paper-2012

  • question_answer
    If \[z\ne 1\] and \[\frac{{{z}^{2}}}{z-1}\] is real, then the point represented by the complex number z lies :   AIEEE  Solved  Paper-2012

    A) either on the real axis or on a circle passing through the origin.

    B) on a circle with centre at the origin.

    C) either on the real axis or on a circle not passing through the origin.

    D) on the imaginary axis.

    Correct Answer: A

    Solution :

                 \[\frac{{{z}^{2}}}{z-1}=\frac{{{\overline{z}}^{2}}}{z-1}\]              \[\Rightarrow z\overline{z}z-{{z}^{2}}=z\overline{z}\overline{z}-{{z}^{2}}\] \[\Rightarrow {{\left| z \right|}^{2}}(z-\overline{z})-(z-\overline{z})(z+\overline{z})=0\] \[\Rightarrow (z-\overline{z})\,\,({{\left| z \right|}^{2}}-(z+\overline{z})=0\] Either \[z=\overline{z}\Rightarrow \] real axis or \[{{\left| z \right|}^{2}}=z+z\Rightarrow z\overline{z}-z-\overline{z}=0\] represents a circle passing through origin.


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