Matemática discreta Exemplos

$[\begin{array}{c} 1 & 0 & 1 \\ 2 & 4 & 2 \\ 0 & 3 & 1 \end{array}]$

Etapa 1

Find the determinant.

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Etapa 1.1

Choose the row or column with the most $0$ elements. If there are no $0$ elements choose any row or column. Multiply every element in row $1$ by its cofactor and add.

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Etapa 1.1.1

Consider the corresponding sign chart.

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

Etapa 1.1.2

The cofactor is the minor with the sign changed if the indices match a $-$ position on the sign chart.

Etapa 1.1.3

The minor for $a_{11}$ is the determinant with row $1$ and column $1$ deleted.

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

Etapa 1.1.4

Multiply element $a_{11}$ by its cofactor.

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

Etapa 1.1.5

The minor for $a_{12}$ is the determinant with row $1$ and column $2$ deleted.

$| \begin{array}{c} 2 & 2 \\ 0 & 1 \end{array} |$

Etapa 1.1.6

Multiply element $a_{12}$ by its cofactor.

$0 | \begin{array}{c} 2 & 2 \\ 0 & 1 \end{array} |$

Etapa 1.1.7

The minor for $a_{13}$ is the determinant with row $1$ and column $3$ deleted.

$| \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.1.8

Multiply element $a_{13}$ by its cofactor.

$1 | \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.1.9

Add the terms together.

$1 | \begin{array}{c} 4 & 2 \\ 3 & 1 \end{array} | + 0 | \begin{array}{c} 2 & 2 \\ 0 & 1 \end{array} | + 1 | \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.2

Multiplique $0$ por $| \begin{array}{c} 2 & 2 \\ 0 & 1 \end{array} |$ .

$1 | \begin{array}{c} 4 & 2 \\ 3 & 1 \end{array} | + 0 + 1 | \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.3

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

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Etapa 1.3.1

O determinante de uma matriz $2 \times 2$ pode ser encontrado ao usar a fórmula $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$1 (4 \cdot 1 - 3 \cdot 2) + 0 + 1 | \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.3.2

Simplifique o determinante.

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Etapa 1.3.2.1

Simplifique cada termo.

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Etapa 1.3.2.1.1

Multiplique $4$ por $1$ .

$1 (4 - 3 \cdot 2) + 0 + 1 | \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.3.2.1.2

Multiplique $- 3$ por $2$ .

$1 (4 - 6) + 0 + 1 | \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.3.2.2

Subtraia $6$ de $4$ .

$1 \cdot - 2 + 0 + 1 | \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$

Etapa 1.4

Avalie $| \begin{array}{c} 2 & 4 \\ 0 & 3 \end{array} |$ .

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Etapa 1.4.1

O determinante de uma matriz $2 \times 2$ pode ser encontrado ao usar a fórmula $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$1 \cdot - 2 + 0 + 1 (2 \cdot 3 + 0 \cdot 4)$

Etapa 1.4.2

Simplifique o determinante.

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Etapa 1.4.2.1

Simplifique cada termo.

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Etapa 1.4.2.1.1

Multiplique $2$ por $3$ .

$1 \cdot - 2 + 0 + 1 (6 + 0 \cdot 4)$

Etapa 1.4.2.1.2

Multiplique $0$ por $4$ .

$1 \cdot - 2 + 0 + 1 (6 + 0)$

Etapa 1.4.2.2

Some $6$ e $0$ .

$1 \cdot - 2 + 0 + 1 \cdot 6$

Etapa 1.5

Simplifique o determinante.

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Etapa 1.5.1

Simplifique cada termo.

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Etapa 1.5.1.1

Multiplique $- 2$ por $1$ .

$- 2 + 0 + 1 \cdot 6$

Etapa 1.5.1.2

Multiplique $6$ por $1$ .

$- 2 + 0 + 6$

Etapa 1.5.2

Some $- 2$ e $0$ .

$- 2 + 6$

Etapa 1.5.3

Some $- 2$ e $6$ .

$4$

Etapa 2

Since the determinant is non-zero, the inverse exists.

Etapa 3

Set up a $3 \times 6$ matrix where the left half is the original matrix and the right half is its identity matrix.

$[\begin{array}{c} 1 & 0 & 1 & 1 & 0 & 0 \\ 2 & 4 & 2 & 0 & 1 & 0 \\ 0 & 3 & 1 & 0 & 0 & 1 \end{array}]$

Etapa 4

Encontre a forma escalonada reduzida por linhas.

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Etapa 4.1

Perform the row operation $R_{2} = R_{2} - 2 R_{1}$ to make the entry at $2, 1$ a $0$ .

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Etapa 4.1.1

Perform the row operation $R_{2} = R_{2} - 2 R_{1}$ to make the entry at $2, 1$ a $0$ .

$[\begin{array}{c} 1 & 0 & 1 & 1 & 0 & 0 \\ 2 - 2 \cdot 1 & 4 - 2 \cdot 0 & 2 - 2 \cdot 1 & 0 - 2 \cdot 1 & 1 - 2 \cdot 0 & 0 - 2 \cdot 0 \\ 0 & 3 & 1 & 0 & 0 & 1 \end{array}]$

Etapa 4.1.2

Simplifique $R_{2}$ .

$[\begin{array}{c} 1 & 0 & 1 & 1 & 0 & 0 \\ 0 & 4 & 0 & - 2 & 1 & 0 \\ 0 & 3 & 1 & 0 & 0 & 1 \end{array}]$

Etapa 4.2

Multiply each element of $R_{2}$ by $\frac{1}{4}$ to make the entry at $2, 2$ a $1$ .

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Etapa 4.2.1

Multiply each element of $R_{2}$ by $\frac{1}{4}$ to make the entry at $2, 2$ a $1$ .

$[\begin{array}{c} 1 & 0 & 1 & 1 & 0 & 0 \\ \frac{0}{4} & \frac{4}{4} & \frac{0}{4} & \frac{- 2}{4} & \frac{1}{4} & \frac{0}{4} \\ 0 & 3 & 1 & 0 & 0 & 1 \end{array}]$

Etapa 4.2.2

Simplifique $R_{2}$ .

$[\begin{array}{c} 1 & 0 & 1 & 1 & 0 & 0 \\ 0 & 1 & 0 & - \frac{1}{2} & \frac{1}{4} & 0 \\ 0 & 3 & 1 & 0 & 0 & 1 \end{array}]$

Etapa 4.3

Perform the row operation $R_{3} = R_{3} - 3 R_{2}$ to make the entry at $3, 2$ a $0$ .

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Etapa 4.3.1

Perform the row operation $R_{3} = R_{3} - 3 R_{2}$ to make the entry at $3, 2$ a $0$ .

$[\begin{array}{c} 1 & 0 & 1 & 1 & 0 & 0 \\ 0 & 1 & 0 & - \frac{1}{2} & \frac{1}{4} & 0 \\ 0 - 3 \cdot 0 & 3 - 3 \cdot 1 & 1 - 3 \cdot 0 & 0 - 3 (- \frac{1}{2}) & 0 - 3 (\frac{1}{4}) & 1 - 3 \cdot 0 \end{array}]$

Etapa 4.3.2

Simplifique $R_{3}$ .

$[\begin{array}{c} 1 & 0 & 1 & 1 & 0 & 0 \\ 0 & 1 & 0 & - \frac{1}{2} & \frac{1}{4} & 0 \\ 0 & 0 & 1 & \frac{3}{2} & - \frac{3}{4} & 1 \end{array}]$

Etapa 4.4

Perform the row operation $R_{1} = R_{1} - R_{3}$ to make the entry at $1, 3$ a $0$ .

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Etapa 4.4.1

Perform the row operation $R_{1} = R_{1} - R_{3}$ to make the entry at $1, 3$ a $0$ .

$[\begin{array}{c} 1 - 0 & 0 - 0 & 1 - 1 & 1 - \frac{3}{2} & 0 + \frac{3}{4} & 0 - 1 \\ 0 & 1 & 0 & - \frac{1}{2} & \frac{1}{4} & 0 \\ 0 & 0 & 1 & \frac{3}{2} & - \frac{3}{4} & 1 \end{array}]$

Etapa 4.4.2

Simplifique $R_{1}$ .

$[\begin{array}{c} 1 & 0 & 0 & - \frac{1}{2} & \frac{3}{4} & - 1 \\ 0 & 1 & 0 & - \frac{1}{2} & \frac{1}{4} & 0 \\ 0 & 0 & 1 & \frac{3}{2} & - \frac{3}{4} & 1 \end{array}]$

Etapa 5

The right half of the reduced row echelon form is the inverse.

$[\begin{array}{c} - \frac{1}{2} & \frac{3}{4} & - 1 \\ - \frac{1}{2} & \frac{1}{4} & 0 \\ \frac{3}{2} & - \frac{3}{4} & 1 \end{array}]$