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det(\left(\begin{matrix}-3&0&6\\5&4&3\\2&-1&1\end{matrix}\right))
Find the determinant of the matrix using the method of diagonals.
\left(\begin{matrix}-3&0&6&-3&0\\5&4&3&5&4\\2&-1&1&2&-1\end{matrix}\right)
Extend the original matrix by repeating the first two columns as the fourth and fifth columns.
-3\times 4+6\times 5\left(-1\right)=-42
Starting at the upper left entry, multiply down along the diagonals, and add the resulting products.
2\times 4\times 6-3\left(-3\right)=57
Starting at the lower left entry, multiply up along the diagonals, and add the resulting products.
-42-57
Subtract the sum of the upward diagonal products from the sum of the downward diagonal products.
-99
Subtract 57 from -42.
det(\left(\begin{matrix}-3&0&6\\5&4&3\\2&-1&1\end{matrix}\right))
Find the determinant of the matrix using the method of expansion by minors (also known as expansion by cofactors).
-3det(\left(\begin{matrix}4&3\\-1&1\end{matrix}\right))+6det(\left(\begin{matrix}5&4\\2&-1\end{matrix}\right))
To expand by minors, multiply each element of the first row by its minor, which is the determinant of the 2\times 2 matrix created by deleting the row and column containing that element, then multiply by the element's position sign.
-3\left(4-\left(-3\right)\right)+6\left(5\left(-1\right)-2\times 4\right)
For the 2\times 2 matrix \left(\begin{matrix}a&b\\c&d\end{matrix}\right), the determinant is ad-bc.
-3\times 7+6\left(-13\right)
Simplify.
-99
Add the terms to obtain the final result.