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

  • question_answer
    If \[z=\sqrt{2}-i\sqrt{2}\] is rotated through an angle \[45{}^\circ \] in the anti-clockwise direction about the origin, then the coordinates of its new position are [Kerala (Engg.) 2005]

    A) (2, 0)

    B) (\[\sqrt{2},\,\sqrt{2}\])

    C) \[(\sqrt{2},\,-\sqrt{2}\])

    D) \[(\sqrt{2},0)\]

    E) (4, 0)

    Correct Answer: D

    Solution :

    \[z=\sqrt{2}-i\sqrt{2}\] Here, \[\theta ={{\tan }^{-1}}\left( \frac{-\sqrt{2}}{\sqrt{2}} \right)\] = \[{{\tan }^{-1}}(-1)\] = \[{{135}^{o}}\] Now, rotate z in opposite direction with 45° angle \[\therefore \] \[\theta =180{}^\circ \] \[\therefore \] \[\theta ={{\tan }^{-1}}(0)={{\tan }^{-1}}\left( \frac{0}{\sqrt{2}} \right)\] Þ Hence \[x=\sqrt{2}\] and\[y=0\].


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