JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Conjugate, Modulus and Argument of complex number

  • question_answer
    If \[z\] is a complex number such that \[{{z}^{2}}={{(\bar{z})}^{2}},\] then

    A) \[z\]is purely real

    B) \[z\]is purely imaginary

    C) Either \[z\]is purely real or purely imaginary

    D) None of these

    Correct Answer: C

    Solution :

    Let\[z=x+iy\], then its conjugate  \[\overline{z}=x-iy\] Given that \[{{z}^{2}}={{(\overline{z})}^{2}}\] Þ \[{{x}^{2}}-{{y}^{2}}+2ixy={{x}^{2}}-{{y}^{2}}-2ixy\]Þ \[4ixy=0\] If  \[x\ne 0\] then \[y=0\]and if \[y\ne 0\]then \[x=0\]


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