JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Geometry of complex numbers

  • question_answer
    A circle whose radius is r and centre \[{{z}_{0}}\], then the equation of the circle is [RPET 2000]

    A) \[z\bar{z}-z{{\bar{z}}_{0}}-\bar{z}{{z}_{0}}+{{z}_{0}}{{\bar{z}}_{0}}={{r}^{2}}\]

    B) \[z\bar{z}+z{{\bar{z}}_{0}}-\bar{z}{{z}_{0}}+{{z}_{0}}{{\bar{z}}_{0}}={{r}^{2}}\]

    C) \[z\bar{z}-z{{\bar{z}}_{0}}+\bar{z}{{z}_{0}}-{{z}_{0}}{{\bar{z}}_{0}}={{r}^{2}}\]

    D) None of these

    Correct Answer: A

    Solution :

    Equation of circle  \[|z-{{z}_{0}}{{|}^{2}}={{r}^{2}}\] \[\Rightarrow \,(z-{{z}_{0}})\,(\overline{z-{{z}_{0}}})={{r}^{2}}\]\[\Rightarrow \,(z-{{z}_{0}})\,(\bar{z}-{{\bar{z}}_{0}})=\,{{r}^{2}}\] \[z\bar{z}-z{{\bar{z}}_{0}}-\bar{z}{{z}_{0}}+{{z}_{0}}{{\bar{z}}_{0}}={{r}^{2}}\].


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