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

  • question_answer
    The values of  \[z\]for which \[|z+i|\,=\,|z-i|\] are [Bihar CEE 1994]

    A) Any real number

    B) Any complex number

    C) Any natural number

    D) None of these

    Correct Answer: A

    Solution :

    Let  \[z=x+iy\] ......(i) Given \[|z+i|\,=\,|z-i|\] or   \[|x+iy+i|\,=\,|x+iy-i|\]  or   \[|x+i(y+1)|\,=\,|x+i(y-1)|\] or  \[\sqrt{{{x}^{2}}+\,{{(y+1)}^{2}}}=\sqrt{{{x}^{2}}+{{(y-1)}^{2}}}\] or  \[{{x}^{2}}+{{(y+1)}^{2}}={{x}^{2}}+{{(y-1)}^{2}}\] or  \[{{y}^{2}}+2y+1={{y}^{2}}-2y+1\]or \[4y=0\]or \[y=0\] Hence from (i), we get\[z=x\], where \[x\] is any real number.


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