JEE Main & Advanced JEE Main Paper (Held on 10-4-2019 Afternoon)

  • question_answer
    If z and w are two complex numbers such that \[\left| zw \right|=1\]and \[arg\left( z \right)arg\left( \text{w} \right)=\frac{\pi }{2},\]then : [JEE Main 10-4-2019 Afternoon]

    A) \[\overline{z}\,\text{w}=i\]                

    B) \[\overline{z}\,\text{w}=-i\]

    C) \[\,z\,\overline{\text{w}}=\frac{1-i}{\sqrt{2}}\]                   

    D) \[\,z\,\overline{\text{w}}=\frac{-1+i}{\sqrt{2}}\]

    Correct Answer: B

    Solution :

    \[|z|.|\text{w}|=1\,\,\,\,\,\,\,\,\,z=r{{e}^{i(\theta +\pi /2)}}\]and\[\text{w}\,\text{=}\frac{1}{r}{{e}^{i\theta }}\]           \[\overline{z.}\text{w}\,\text{=}{{e}^{-i\theta +\pi /2}}.{{e}^{i\theta }}={{e}^{-i}}^{(\pi /2)}=-i\]           \[z.\overline{\text{w}}\,\text{=}{{e}^{i(\theta +\pi /2)}}.{{e}^{-i\theta }}={{e}^{i}}^{(\pi /2)}=i\]


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