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

  • question_answer
    The points \[1+3i,\,5+i\] and \[3+2i\] in the complex plane are [MP PET 1987]

    A) Vertices of a right angled triangle

    B) Collinear

    C) Vertices of an obtuse angled triangle

    D) Vertices of an equilateral triangle

    Correct Answer: B

    Solution :

    Let \[{{z}_{1}}=1+3i,{{z}_{2}}=5+i\] and \[{{z}_{3}}=3+2i\] Then area of triangle \[A=\frac{1}{2}\left| \begin{matrix}    {{x}_{1}} & {{y}_{1}} & 1  \\    {{x}_{2}} & {{y}_{2}} & 1  \\    {{x}_{3}} & {{y}_{3}} & 1  \\ \end{matrix} \right|=\frac{1}{2}\left| \begin{matrix}    1 & 3 & 1  \\    5 & 1 & 1  \\    3 & 2 & 1  \\ \end{matrix} \right|=0\] Hence \[{{z}_{1}},{{z}_{2}}\] and \[{{z}_{3}}\] are collinear.


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