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

  • question_answer
    \[\left| \frac{1}{2}({{z}_{1}}+{{z}_{2}})+\sqrt{{{z}_{1}}{{z}_{2}}} \right|+\left| \frac{1}{2}({{z}_{1}}+{{z}_{2}})-\sqrt{{{z}_{1}}{{z}_{2}}} \right|\] =

    A) \[|{{z}_{1}}+{{z}_{2}}|\]

    B) \[|{{z}_{1}}-{{z}_{2}}|\]

    C) \[|{{z}_{1}}+{{z}_{2}}|\]

    D) \[|{{z}_{1}}|-|{{z}_{2}}|\]

    Correct Answer: C

    Solution :

    R.H.S = \[\frac{1}{2}|{{(\sqrt{{{z}_{1}}}+\sqrt{{{z}_{2}}})}^{2}}|+\frac{1}{2}|{{(\sqrt{{{z}_{1}}}-\sqrt{{{z}_{2}}})}^{2}}|\] \[=\frac{1}{2}|\sqrt{{{z}_{1}}}+\sqrt{{{z}_{2}}}{{|}^{2}}+\frac{1}{2}|\sqrt{{{z}_{1}}}-\sqrt{{{z}_{2}}}{{|}^{2}}\] \[\{\because |{{z}^{2}}|=|z{{|}^{2}}\}\] \[=\frac{1}{2}2\,[|\sqrt{{{z}_{1}}}{{|}^{2}}+|\sqrt{{{z}_{2}}}{{|}^{2}}]=|{{z}_{1}}|+|{{z}_{2}}|\]


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