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

  • question_answer
    If \[{{z}_{1}},{{z}_{2}},{{z}_{3}},{{z}_{4}}\] are the affixes of four points in the Argand plane and \[z\] is the affix of a point such that \[|z-{{z}_{1}}|\,=\,|z-{{z}_{2}}|\,=\,|z-{{z}_{3}}|\,=|z-{{z}_{4}}|\], then \[{{z}_{1}},{{z}_{2}},{{z}_{3}},{{z}_{4}}\] are

    A) Concyclic

    B) Vertices of a parallelogram

    C) Vertices of a rhombus

    D) In a straight line

    Correct Answer: A

    Solution :

    We have \[|z-{{z}_{1}}|\,=\,|z-{{z}_{2}}|\,=\,|z-{{z}_{3}}|\,=\,|z-{{z}_{4}}|\] Therefore the point having affix \[z\] is equidistant from the four points having affixes \[{{z}_{1}},{{z}_{2}},{{z}_{3}},{{z}_{4}}\].  Thus \[z\] is the affix of either the centre of a circle or the point of intersection of diagonals of a square or rectangle. Therefore \[{{z}_{1}},{{z}_{2}},{{z}_{3}},{{z}_{4}}\] are either concyclic or vertices of a square. Hence \[{{z}_{1}},{{z}_{2}},{{z}_{3}},{{z}_{4}}\] are concyclic.


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