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det(\left(\begin{matrix}1&2&3\\-2&3&5\\5&3&4\end{matrix}\right))
Find the determinant of the matrix using the method of diagonals.
\left(\begin{matrix}1&2&3&1&2\\-2&3&5&-2&3\\5&3&4&5&3\end{matrix}\right)
Extend the original matrix by repeating the first two columns as the fourth and fifth columns.
3\times 4+2\times 5\times 5+3\left(-2\right)\times 3=44
Starting at the upper left entry, multiply down along the diagonals, and add the resulting products.
5\times 3\times 3+3\times 5+4\left(-2\right)\times 2=44
Starting at the lower left entry, multiply up along the diagonals, and add the resulting products.
44-44
Subtract the sum of the upward diagonal products from the sum of the downward diagonal products.
0
Subtract 44 from 44.
det(\left(\begin{matrix}1&2&3\\-2&3&5\\5&3&4\end{matrix}\right))
Find the determinant of the matrix using the method of expansion by minors (also known as expansion by cofactors).
det(\left(\begin{matrix}3&5\\3&4\end{matrix}\right))-2det(\left(\begin{matrix}-2&5\\5&4\end{matrix}\right))+3det(\left(\begin{matrix}-2&3\\5&3\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\times 4-3\times 5-2\left(-2\times 4-5\times 5\right)+3\left(-2\times 3-5\times 3\right)
For the 2\times 2 matrix \left(\begin{matrix}a&b\\c&d\end{matrix}\right), the determinant is ad-bc.
-3-2\left(-33\right)+3\left(-21\right)
Simplify.
0
Add the terms to obtain the final result.