JEE Main & Advanced Sample Paper JEE Main Sample Paper-14

  • question_answer
    If \[|z|\,=5,\] then the area of the triangle whose length of the sides are equal to \[|z|,\,\,|\beta z|\] and \[|z+\beta z+{{\beta }^{2}}z+{{\beta }^{3}}z|\] (where (\[\beta \] is fifth root of unit y and z be a complex number) is

    A)  \[\frac{25\sqrt{3}}{2}\]                

    B)  \[\frac{25\sqrt{3}}{4}\]

    C)  \[\frac{75\sqrt{3}}{2}\]                

    D)  \[\frac{75\sqrt{3}}{4}\]

    Correct Answer: B

    Solution :

     Given, \[|z|\,=5,\,\,|\beta z|\,=5\]       \[(\because \,\,|\beta |\,=1)\] and \[|z+\beta z+{{\beta }^{2}}z+{{\beta }^{3}}z|\] \[=\,|z||1+\beta +{{\beta }^{2}}+{{\beta }^{3}}|\] \[=\,|z||-{{\beta }^{4}}|\]          \[(\because \,1+\beta +{{\beta }^{2}}+{{\beta }^{3}}+{{\beta }^{4}}=0)\] = 5 So, trinagle will be an equilateral triangle. \[\therefore \]  Area \[=\frac{\sqrt{3}}{4}|z{{|}^{2}}=\frac{\sqrt{3}}{4}\times 25=\frac{25\sqrt{3}}{4}\]


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