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

  • question_answer
    The solution of the equation \[|z|-z=1+2i\] is [MP PET 1993]

    A) \[2-\frac{3}{2}i\]

    B) \[\frac{3}{2}+2i\]

    C) \[\frac{3}{2}-2i\]

    D) \[-2+\frac{3}{2}i\]

    Correct Answer: C

    Solution :

    \[|z|-z=1+2i\] Let \[z=x+iy\], therefore \[|x+iy|-(x+iy)=1+2i\] Equating real and imaginary parts, we get \[\sqrt{{{x}^{2}}+{{y}^{2}}}-x=1\]and \[y=-2\]Þ\[x=\frac{3}{2}\] Hence complex number\[z=\frac{3}{2}-2i\]. Trick:  Since \[\left| \frac{3}{2}-2i \right|-\left( \frac{3}{2}-2i \right)\] \[=\sqrt{\frac{9}{4}+4}-\frac{3}{2}+2i=\frac{5}{2}-\frac{3}{2}+2i=1+2i\]


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