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

  • question_answer
    The number of solutions of the equation \[{{z}^{2}}+\bar{z}=0\] is

    A) 1

    B) 2

    C) 3

    D) 4

    Correct Answer: D

    Solution :

    Let \[z=x+iy,\] so that \[\overline{z}=x-iy,\] therefore \[{{z}^{2}}+\overline{z}=0\,\Leftrightarrow ({{x}^{2}}-{{y}^{2}}+x)+i\,(2xy-y)=0\] Equating real and imaginary parts, we get \[{{x}^{2}}-{{y}^{2}}+x=0\]    .....(i) and \[2xy-y=0\]  Þ \[y=0\]or \[x=\frac{1}{2}\] If \[y=0\], then (i) gives \[{{x}^{2}}+x=0\,\,\Rightarrow x=0\]or \[x=-1\] If \[x=\frac{1}{2},\] Then \[{{x}^{2}}-{{y}^{2}}+x=0\]Þ\[{{y}^{2}}=\frac{1}{4}+\frac{1}{2}=\frac{3}{4}\]Þ\[y=\pm \frac{\sqrt{3}}{2}\] Hence, there are four solutions in all.


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