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

  • question_answer
    Let \[{{z}_{1}}\] and  \[{{z}_{2}}\] be two complex numbers such that  \[\frac{{{z}_{1}}}{{{z}_{2}}}+\frac{{{z}_{2}}}{{{z}_{1}}}=1\]. Then

    A) \[{{z}_{1}},{{z}_{2}}\]are collinear

    B) \[{{z}_{1}},{{z}_{2}}\]and the origin form a right angled triangle

    C) \[{{z}_{1}},{{z}_{2}}\]and the origin form an equilateral triangle

    D) None of these

    Correct Answer: C

    Solution :

    We have \[\frac{{{z}_{1}}}{{{z}_{2}}}+\frac{{{z}_{2}}}{{{z}_{1}}}=1\Rightarrow z_{1}^{2}+z_{2}^{2}={{z}_{1}}{{z}_{2}}\] Þ  \[z_{1}^{2}+z_{2}^{2}+z_{3}^{2}={{z}_{1}}{{z}_{2}}+{{z}_{1}}{{z}_{3}}+{{z}_{2}}{{z}_{3}},\]where\[{{z}_{3}}=0\] Þ \[{{z}_{1}},{{z}_{2}}\] and the origin \[(\because {{z}_{3}}=0)\] form an equilateral triangle.


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