The cofactor of the element \( a_{21} \) in the expansion of
\[
\Delta = \begin{vmatrix} 1 & 4 & 4 -3 & 5 & 9 2 & 1 & 2 \end{vmatrix}
\]
is
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The cofactor of an element in a matrix is calculated by multiplying the determinant of its minor by \( (-1)^{i+j} \), where \( i \) and \( j \) are the row and column indices of the element.