Finite Math Examples

⎡ ⎢ ⎣ \begin{matrix} 4 & 3 & 1 3 & 2 & 1 4 & 3 & 4 \end{matrix} ⎤ ⎥ ⎦

$[\begin{array}{c} 4 & 3 & 1 \\ 3 & 2 & 1 \\ 4 & 3 & 4 \end{array}]$

Step 1

Choose the row or column with the most

0

$0$ elements. If there are no

0

$0$ elements choose any row or column. Multiply every element in row

1

$1$ by its cofactor and add.

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Step 1.1

Consider the corresponding sign chart.

∣ ∣ ∣ ∣ \begin{matrix} + & - & + - & + & - + & - & + \end{matrix} ∣ ∣ ∣ ∣

$| \begin{array}{c} + & - & + \\ - & + & - \\ + & - & + \end{array} |$

Step 1.2

The cofactor is the minor with the sign changed if the indices match a

-

$-$ position on the sign chart.

Step 1.3

The minor for

a_{11}

$a_{11}$ is the determinant with row

1

$1$ and column

1

$1$ deleted.

∣ ∣ ∣ \begin{matrix} 2 & 1 3 & 4 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 2 & 1 \\ 3 & 4 \end{array} |$

Step 1.4

Multiply element

a_{11}

$a_{11}$ by its cofactor.

4 ∣ ∣ ∣ \begin{matrix} 2 & 1 3 & 4 \end{matrix} ∣ ∣ ∣

$4 | \begin{array}{c} 2 & 1 \\ 3 & 4 \end{array} |$

Step 1.5

The minor for

a_{12}

$a_{12}$ is the determinant with row

1

$1$ and column

2

$2$ deleted.

∣ ∣ ∣ \begin{matrix} 3 & 1 4 & 4 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} |$

Step 1.6

Multiply element

a_{12}

$a_{12}$ by its cofactor.

- 3 ∣ ∣ ∣ \begin{matrix} 3 & 1 4 & 4 \end{matrix} ∣ ∣ ∣

$- 3 | \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} |$

Step 1.7

The minor for

a_{13}

$a_{13}$ is the determinant with row

1

$1$ and column

3

$3$ deleted.

∣ ∣ ∣ \begin{matrix} 3 & 2 4 & 3 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 1.8

Multiply element

a_{13}

$a_{13}$ by its cofactor.

1 ∣ ∣ ∣ \begin{matrix} 3 & 2 4 & 3 \end{matrix} ∣ ∣ ∣

$1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 1.9

Add the terms together.

4 ∣ ∣ ∣ \begin{matrix} 2 & 1 3 & 4 \end{matrix} ∣ ∣ ∣ - 3 ∣ ∣ ∣ \begin{matrix} 3 & 1 4 & 4 \end{matrix} ∣ ∣ ∣ + 1 ∣ ∣ ∣ \begin{matrix} 3 & 2 4 & 3 \end{matrix} ∣ ∣ ∣

$4 | \begin{array}{c} 2 & 1 \\ 3 & 4 \end{array} | - 3 | \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} | + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 2

Evaluate

$| \begin{array}{c} 2 & 1 \\ 3 & 4 \end{array} |$ .

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Step 2.1

The determinant of a

$2 \times 2$ matrix can be found using the formula

$| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$4 (2 \cdot 4 - 3 \cdot 1) - 3 | \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} | + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 2.2

Simplify the determinant.

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Step 2.2.1

Simplify each term.

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Step 2.2.1.1

Multiply

$2$ by

$4$ .

$4 (8 - 3 \cdot 1) - 3 | \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} | + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 2.2.1.2

Multiply

$- 3$ by

$1$ .

$4 (8 - 3) - 3 | \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} | + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 2.2.2

Subtract

$3$ from

$8$ .

$4 \cdot 5 - 3 | \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} | + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 3

Evaluate

$| \begin{array}{c} 3 & 1 \\ 4 & 4 \end{array} |$ .

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Step 3.1

The determinant of a

$2 \times 2$ matrix can be found using the formula

$| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$4 \cdot 5 - 3 (3 \cdot 4 - 4 \cdot 1) + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 3.2

Simplify the determinant.

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Step 3.2.1

Simplify each term.

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Step 3.2.1.1

Multiply

$3$ by

$4$ .

$4 \cdot 5 - 3 (12 - 4 \cdot 1) + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 3.2.1.2

Multiply

$- 4$ by

$1$ .

$4 \cdot 5 - 3 (12 - 4) + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 3.2.2

Subtract

$4$ from

$12$ .

$4 \cdot 5 - 3 \cdot 8 + 1 | \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$

Step 4

Evaluate

$| \begin{array}{c} 3 & 2 \\ 4 & 3 \end{array} |$ .

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Step 4.1

The determinant of a

$2 \times 2$ matrix can be found using the formula

$| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$4 \cdot 5 - 3 \cdot 8 + 1 (3 \cdot 3 - 4 \cdot 2)$

Step 4.2

Simplify the determinant.

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Step 4.2.1

Simplify each term.

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Step 4.2.1.1

Multiply

$3$ by

$3$ .

$4 \cdot 5 - 3 \cdot 8 + 1 (9 - 4 \cdot 2)$

Step 4.2.1.2

Multiply

$- 4$ by

$2$ .

$4 \cdot 5 - 3 \cdot 8 + 1 (9 - 8)$

Step 4.2.2

Subtract

$8$ from

$9$ .

$4 \cdot 5 - 3 \cdot 8 + 1 \cdot 1$

Step 5

Simplify the determinant.

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Step 5.1

Simplify each term.

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Step 5.1.1

Multiply

$4$ by

$5$ .

$20 - 3 \cdot 8 + 1 \cdot 1$

Step 5.1.2

Multiply

$- 3$ by

$8$ .

$20 - 24 + 1 \cdot 1$

Step 5.1.3

Multiply

$1$ by

$1$ .

$20 - 24 + 1$

Step 5.2

Subtract

$24$ from

$20$ .

$- 4 + 1$

Step 5.3

Add

$- 4$ and

$1$ .

$- 3$

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