Solve {lll}{1}&{2}&{3}{2}&{4}&{5}{3}&{2}&{1}

$$\left( \begin{array} { l l l } { 1 } & { 2 } & { 3 } \\ { 2 } & { 4 } & { 5 } \\ { 3 } & { 2 } & { 1 } \end{array} \right)$$

Calculate Determinant

$$-4$$

Steps Using Sarrus' Rule

Find the determinant of the matrix using the method of diagonals.

$$det(\left(\begin{matrix}1&2&3\\2&4&5\\3&2&1\end{matrix}\right))$$

Extend the original matrix by repeating the first two columns as the fourth and fifth columns.

$$\left(\begin{matrix}1&2&3&1&2\\2&4&5&2&4\\3&2&1&3&2\end{matrix}\right)$$

Starting at the upper left entry, multiply down along the diagonals, and add the resulting products.

$$4+2\times 5\times 3+3\times 2\times 2=46$$

Starting at the lower left entry, multiply up along the diagonals, and add the resulting products.

$$3\times 4\times 3+2\times 5+2\times 2=50$$

Subtract the sum of the upward diagonal products from the sum of the downward diagonal products.

$$46-50$$

Subtract 50 from 46.

$$-4$$

Steps Using Expansion by Minors

Find the determinant of the matrix using the method of expansion by minors (also known as expansion by cofactors).

$$det(\left(\begin{matrix}1&2&3\\2&4&5\\3&2&1\end{matrix}\right))$$

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.

$$det(\left(\begin{matrix}4&5\\2&1\end{matrix}\right))-2det(\left(\begin{matrix}2&5\\3&1\end{matrix}\right))+3det(\left(\begin{matrix}2&4\\3&2\end{matrix}\right))$$

For the 2\times 2 matrix \left(\begin{matrix}a&b\\c&d\end{matrix}\right), the determinant is ad-bc.

$$4-2\times 5-2\left(2-3\times 5\right)+3\left(2\times 2-3\times 4\right)$$

Simplify.

$$-6-2\left(-13\right)+3\left(-8\right)$$

Add the terms to obtain the final result.

$$-4$$

Evaluate

$$\left(\begin{matrix}1&2&3\\2&4&5\\3&2&1\end{matrix}\right)$$