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3 and 4 .Determinants and Matrices
easy
If $\omega $ is a complex cube root of unity, then the determinant $\left| {\,\begin{array}{*{20}{c}}2&{2\omega }&{ - {\omega ^2}}\\1&1&1\\1&{ - 1}&0\end{array}\,} \right| = $
A
$0$
B
$1$
C
$-1$
D
None of these
Solution
(a) $\Delta \equiv \left| {\,\begin{array}{*{20}{c}}2&{2\omega }&{ – {\omega ^2}}\\1&1&1\\1&{ – 1}&0\end{array}\,} \right| = \left| {\,\begin{array}{*{20}{c}}{2 + 2\omega + 2{\omega ^2}}&{2\omega }&{ – {\omega ^2}}\\{1 + 1 – 2}&1&1\\{1 – 1 – 0}&{ – 1}&0\end{array}\,} \right|$
$({C_1} \to {C_1} + {C_2} – 2{C_3})$
= $\left| {\,\begin{array}{*{20}{c}}0&{2\omega }&{ – {\omega ^2}}\\0&1&1\\0&{ – 1}&0\end{array}\,} \right|\, = \,0$.
Standard 12
Mathematics