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

  • question_answer
    If  \[|{{z}_{1}}+{{z}_{2}}|=|{{z}_{1}}-{{z}_{2}}|\], then the difference in the amplitudes of \[{{z}_{1}}\] and \[{{z}_{2}}\] is [EAMCET 1985]

    A) \[\frac{\pi }{4}\]

    B) \[\frac{\pi }{3}\]

    C) \[\frac{\pi }{2}\]

    D) 0

    Correct Answer: C

    Solution :

    Squaring the given relations implies that \[{{x}_{1}}{{x}_{2}}+{{y}_{1}}{{y}_{2}}=0\] Now \[amp\,\,{{z}_{1}}-amp\,\,{{z}_{2}}={{\tan }^{-1}}\frac{{{y}_{1}}}{{{x}_{1}}}-{{\tan }^{-1}}\frac{{{y}_{2}}}{{{x}_{2}}}\] \[={{\tan }^{-1}}\frac{\frac{{{y}_{1}}}{{{x}_{1}}}-\frac{{{y}_{2}}}{{{x}_{2}}}}{1+\frac{{{y}_{1}}{{y}_{2}}}{{{x}_{1}}{{x}_{2}}}}={{\tan }^{-1}}\frac{{{y}_{1}}{{x}_{2}}-{{y}_{2}}{{x}_{1}}}{{{x}_{1}}{{x}_{2}}+{{y}_{1}}{{y}_{2}}}\]\[={{\tan }^{-1}}\infty =\frac{\pi }{2}\].


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