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QJEEM23Ma032e: JEE Main 2023 Mathematics - Class 11 JEEM23Ma032e Solution

The value of (1+sin⁡2π9+icos⁡2π91+sin⁡2π9−icos⁡2π9)3{\left( {{{1 + \sin {{2\pi } \over 9} + i\cos {{2\pi } \over 9}} \over {1 + \sin {{2\pi } \over 9} - i\cos {{2\pi } \over 9}}}} \right)^3} is

Multiple Choice Options

  • A −12(1−i3)- {1 \over 2}\left( {1 - i\sqrt 3 } \right)
  • B −12(3−i)- {1 \over 2}\left( {\sqrt 3 - i} \right)
  • C 12(1−i3){1 \over 2}\left( {1 - i\sqrt 3 } \right)
  • D 12(3+i){1 \over 2}\left( {\sqrt 3 + i} \right)

Step-by-Step Verified Solution

z=(1+sin⁡2π9+icos⁡2π91+sin⁡2π9−icos⁡2π9)3z=\left(\frac{1+\sin \frac{2 \pi}{9}+i \cos \frac{2 \pi}{9}}{1+\sin \frac{2 \pi}{9}-i \cos \frac{2 \pi}{9}}\right)^{3}

amp;1+sin⁡2π9+icos⁡2π9=1+cos⁡5π18+isin⁡5π18amp;=1+2cos⁡25π36−1+2isin⁡5π36cos⁡5π36amp;=2cos⁡5π36(cos⁡5π36+isin⁡5π36)=2cos⁡5π36ei5π36amp;z=−32+12i=12(i−3)=−12(3−i)\begin{aligned}& 1+\sin \frac{2 \pi}{9}+i \cos \frac{2 \pi}{9}=1+\cos \frac{5 \pi}{18}+i \sin \frac{5 \pi}{18} \\\\& =1+2 \cos ^{2} \frac{5 \pi}{36}-1+2 i \sin \frac{5 \pi}{36} \cos \frac{5 \pi}{36} \\\\& =2 \cos \frac{5 \pi}{36}\left(\cos \frac{5 \pi}{36}+i \sin \frac{5 \pi}{36}\right)=2 \cos \frac{5 \pi}{36} e^{i \frac{5 \pi}{36}} \\\\& z=-\frac{\sqrt{3}}{2}+\frac{1}{2} i=\frac{1}{2}(i-\sqrt{3})=-\frac{1}{2}(\sqrt{3}-i)\end{aligned}

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