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JEE MAIN 2021
31-08-2021 S1
Question
If $a_r=\cos \frac{2 r \pi}{9}+i \sin \frac{2 r \pi}{9}, r=1,2,3, \ldots, \mathrm{i}=\sqrt{-1}$ then the determinant $\left|\begin{array}{lll}a_1 & a_2 & a_3 \\ a_4 & a_5 & a_6 \\ a_7 & a_8 & a_9\end{array}\right|$ is equal to :
Select the correct option:
A
$a_2 a_6-a_4 a_8$
B
$a_9$
C
$a_1 a_9-a_3 a_7$
D
$a_5$
✓ Correct! Well done.
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