Finite Mathematik Beispiele

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

Schritt 1

Find the determinant.

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Schritt 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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Schritt 1.1.1

Consider the corresponding sign chart.

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

Schritt 1.1.2

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

Schritt 1.1.3

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

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

Schritt 1.1.4

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

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

Schritt 1.1.5

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

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

Schritt 1.1.6

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

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

Schritt 1.1.7

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

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

Schritt 1.1.8

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

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

Schritt 1.1.9

Add the terms together.

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

Schritt 1.2

Mutltipliziere $0$ mit $| \begin{array}{c} 2 & 3 \\ 1 & 2 \end{array} |$ .

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

Schritt 1.3

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

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Schritt 1.3.1

Die Determinante einer $2 \times 2$ -Matrix kann mithilfe der Formel $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ bestimmt werden.

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

Schritt 1.3.2

Vereinfache die Determinante.

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Schritt 1.3.2.1

Vereinfache jeden Term.

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Schritt 1.3.2.1.1

Mutltipliziere $3$ mit $3$ .

$4 (9 - 2 \cdot 1) - 4 | \begin{array}{c} 2 & 1 \\ 1 & 3 \end{array} | + 0$

Schritt 1.3.2.1.2

Mutltipliziere $- 2$ mit $1$ .

$4 (9 - 2) - 4 | \begin{array}{c} 2 & 1 \\ 1 & 3 \end{array} | + 0$

Schritt 1.3.2.2

Subtrahiere $2$ von $9$ .

$4 \cdot 7 - 4 | \begin{array}{c} 2 & 1 \\ 1 & 3 \end{array} | + 0$

Schritt 1.4

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

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Schritt 1.4.1

Die Determinante einer $2 \times 2$ -Matrix kann mithilfe der Formel $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ bestimmt werden.

$4 \cdot 7 - 4 (2 \cdot 3 - 1 \cdot 1) + 0$

Schritt 1.4.2

Vereinfache die Determinante.

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Schritt 1.4.2.1

Vereinfache jeden Term.

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Schritt 1.4.2.1.1

Mutltipliziere $2$ mit $3$ .

$4 \cdot 7 - 4 (6 - 1 \cdot 1) + 0$

Schritt 1.4.2.1.2

Mutltipliziere $- 1$ mit $1$ .

$4 \cdot 7 - 4 (6 - 1) + 0$

Schritt 1.4.2.2

Subtrahiere $1$ von $6$ .

$4 \cdot 7 - 4 \cdot 5 + 0$

Schritt 1.5

Vereinfache die Determinante.

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Schritt 1.5.1

Vereinfache jeden Term.

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Schritt 1.5.1.1

Mutltipliziere $4$ mit $7$ .

$28 - 4 \cdot 5 + 0$

Schritt 1.5.1.2

Mutltipliziere $- 4$ mit $5$ .

$28 - 20 + 0$

Schritt 1.5.2

Subtrahiere $20$ von $28$ .

$8 + 0$

Schritt 1.5.3

Addiere $8$ und $0$ .

$8$

Schritt 2

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

Schritt 3

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

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

Schritt 4

Ermittele die normierte Zeilenstufenform.

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Schritt 4.1

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

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Schritt 4.1.1

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

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

Schritt 4.1.2

Vereinfache $R_{1}$ .

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

Schritt 4.2

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

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Schritt 4.2.1

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

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

Schritt 4.2.2

Vereinfache $R_{2}$ .

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

Schritt 4.3

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

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Schritt 4.3.1

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

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

Schritt 4.3.2

Vereinfache $R_{3}$ .

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

Schritt 4.4

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

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Schritt 4.4.1

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

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

Schritt 4.4.2

Vereinfache $R_{3}$ .

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

Schritt 4.5

Multiply each element of $R_{3}$ by $\frac{1}{2}$ to make the entry at $3, 3$ a $1$ .

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Schritt 4.5.1

Multiply each element of $R_{3}$ by $\frac{1}{2}$ to make the entry at $3, 3$ a $1$ .

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

Schritt 4.5.2

Vereinfache $R_{3}$ .

$[\begin{array}{c} 1 & 1 & 0 & \frac{1}{4} & 0 & 0 \\ 0 & 1 & 1 & - \frac{1}{2} & 1 & 0 \\ 0 & 0 & 1 & \frac{1}{8} & - \frac{1}{2} & \frac{1}{2} \end{array}]$

Schritt 4.6

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

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Schritt 4.6.1

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

$[\begin{array}{c} 1 & 1 & 0 & \frac{1}{4} & 0 & 0 \\ 0 - 0 & 1 - 0 & 1 - 1 & - \frac{1}{2} - \frac{1}{8} & 1 + \frac{1}{2} & 0 - \frac{1}{2} \\ 0 & 0 & 1 & \frac{1}{8} & - \frac{1}{2} & \frac{1}{2} \end{array}]$

Schritt 4.6.2

Vereinfache $R_{2}$ .

$[\begin{array}{c} 1 & 1 & 0 & \frac{1}{4} & 0 & 0 \\ 0 & 1 & 0 & - \frac{5}{8} & \frac{3}{2} & - \frac{1}{2} \\ 0 & 0 & 1 & \frac{1}{8} & - \frac{1}{2} & \frac{1}{2} \end{array}]$

Schritt 4.7

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

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Schritt 4.7.1

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

$[\begin{array}{c} 1 - 0 & 1 - 1 & 0 - 0 & \frac{1}{4} + \frac{5}{8} & 0 - \frac{3}{2} & 0 + \frac{1}{2} \\ 0 & 1 & 0 & - \frac{5}{8} & \frac{3}{2} & - \frac{1}{2} \\ 0 & 0 & 1 & \frac{1}{8} & - \frac{1}{2} & \frac{1}{2} \end{array}]$

Schritt 4.7.2

Vereinfache $R_{1}$ .

$[\begin{array}{c} 1 & 0 & 0 & \frac{7}{8} & - \frac{3}{2} & \frac{1}{2} \\ 0 & 1 & 0 & - \frac{5}{8} & \frac{3}{2} & - \frac{1}{2} \\ 0 & 0 & 1 & \frac{1}{8} & - \frac{1}{2} & \frac{1}{2} \end{array}]$

Schritt 5

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

$[\begin{array}{c} \frac{7}{8} & - \frac{3}{2} & \frac{1}{2} \\ - \frac{5}{8} & \frac{3}{2} & - \frac{1}{2} \\ \frac{1}{8} & - \frac{1}{2} & \frac{1}{2} \end{array}]$

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