线性代数示例

⎡ ⎢ ⎣ \begin{matrix} 1 & 2 & 3 2 & 5 & 7 3 & 7 & 9 \end{matrix} ⎤ ⎥ ⎦

$[\begin{array}{c} 1 & 2 & 3 \\ 2 & 5 & 7 \\ 3 & 7 & 9 \end{array}]$

解题步骤 1

Find the determinant.

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解题步骤 1.1

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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解题步骤 1.1.1

Consider the corresponding sign chart.

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

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

解题步骤 1.1.2

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

-

$-$ position on the sign chart.

解题步骤 1.1.3

The minor for

a_{11}

$a_{11}$ is the determinant with row

1

$1$ and column

1

$1$ deleted.

∣ ∣ ∣ \begin{matrix} 5 & 7 7 & 9 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 5 & 7 \\ 7 & 9 \end{array} |$

解题步骤 1.1.4

Multiply element

a_{11}

$a_{11}$ by its cofactor.

1 ∣ ∣ ∣ \begin{matrix} 5 & 7 7 & 9 \end{matrix} ∣ ∣ ∣

$1 | \begin{array}{c} 5 & 7 \\ 7 & 9 \end{array} |$

解题步骤 1.1.5

The minor for

a_{12}

$a_{12}$ is the determinant with row

1

$1$ and column

2

$2$ deleted.

∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} |$

解题步骤 1.1.6

Multiply element

a_{12}

$a_{12}$ by its cofactor.

- 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣

$- 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} |$

解题步骤 1.1.7

The minor for

a_{13}

$a_{13}$ is the determinant with row

1

$1$ and column

3

$3$ deleted.

∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.1.8

Multiply element

a_{13}

$a_{13}$ by its cofactor.

3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.1.9

Add the terms together.

1 ∣ ∣ ∣ \begin{matrix} 5 & 7 7 & 9 \end{matrix} ∣ ∣ ∣ - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 | \begin{array}{c} 5 & 7 \\ 7 & 9 \end{array} | - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

1 ∣ ∣ ∣ \begin{matrix} 5 & 7 7 & 9 \end{matrix} ∣ ∣ ∣ - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 | \begin{array}{c} 5 & 7 \\ 7 & 9 \end{array} | - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.2

计算

∣ ∣ ∣ \begin{matrix} 5 & 7 7 & 9 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 5 & 7 \\ 7 & 9 \end{array} |$ 。

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解题步骤 1.2.1

可以使用公式

∣ ∣ ∣ \begin{matrix} a & b c & d \end{matrix} ∣ ∣ ∣ = a d - c b

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

2 \times 2

$2 \times 2$ 矩阵的行列式。

1 (5 \cdot 9 - 7 \cdot 7) - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 (5 \cdot 9 - 7 \cdot 7) - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.2.2

化简行列式。

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解题步骤 1.2.2.1

化简每一项。

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解题步骤 1.2.2.1.1

将

5

$5$ 乘以

9

$9$ 。

1 (45 - 7 \cdot 7) - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 (45 - 7 \cdot 7) - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.2.2.1.2

将

- 7

$- 7$ 乘以

7

$7$ 。

1 (45 - 49) - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 (45 - 49) - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

1 (45 - 49) - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 (45 - 49) - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.2.2.2

从

45

$45$ 中减去

49

$49$ 。

1 \cdot - 4 - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

1 \cdot - 4 - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

1 \cdot - 4 - 2 ∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣ + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 | \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} | + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.3

计算

∣ ∣ ∣ \begin{matrix} 2 & 7 3 & 9 \end{matrix} ∣ ∣ ∣

$| \begin{array}{c} 2 & 7 \\ 3 & 9 \end{array} |$ 。

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解题步骤 1.3.1

可以使用公式

∣ ∣ ∣ \begin{matrix} a & b c & d \end{matrix} ∣ ∣ ∣ = a d - c b

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

2 \times 2

$2 \times 2$ 矩阵的行列式。

1 \cdot - 4 - 2 (2 \cdot 9 - 3 \cdot 7) + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 (2 \cdot 9 - 3 \cdot 7) + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.3.2

化简行列式。

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解题步骤 1.3.2.1

化简每一项。

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解题步骤 1.3.2.1.1

将

2

$2$ 乘以

9

$9$ 。

1 \cdot - 4 - 2 (18 - 3 \cdot 7) + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 (18 - 3 \cdot 7) + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.3.2.1.2

将

- 3

$- 3$ 乘以

7

$7$ 。

1 \cdot - 4 - 2 (18 - 21) + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 (18 - 21) + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

1 \cdot - 4 - 2 (18 - 21) + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 (18 - 21) + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.3.2.2

从

18

$18$ 中减去

21

$21$ 。

1 \cdot - 4 - 2 \cdot - 3 + 3 ∣ ∣ ∣ \begin{matrix} 2 & 5 3 & 7 \end{matrix} ∣ ∣ ∣

$1 \cdot - 4 - 2 \cdot - 3 + 3 | \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$

解题步骤 1.4

计算

$| \begin{array}{c} 2 & 5 \\ 3 & 7 \end{array} |$ 。

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解题步骤 1.4.1

可以使用公式

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

$2 \times 2$ 矩阵的行列式。

$1 \cdot - 4 - 2 \cdot - 3 + 3 (2 \cdot 7 - 3 \cdot 5)$

解题步骤 1.4.2

化简行列式。

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解题步骤 1.4.2.1

化简每一项。

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解题步骤 1.4.2.1.1

将

$2$ 乘以

$7$ 。

$1 \cdot - 4 - 2 \cdot - 3 + 3 (14 - 3 \cdot 5)$

解题步骤 1.4.2.1.2

将

$- 3$ 乘以

$5$ 。

$1 \cdot - 4 - 2 \cdot - 3 + 3 (14 - 15)$

解题步骤 1.4.2.2

从

$14$ 中减去

$15$ 。

$1 \cdot - 4 - 2 \cdot - 3 + 3 \cdot - 1$

解题步骤 1.5

化简行列式。

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解题步骤 1.5.1

化简每一项。

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解题步骤 1.5.1.1

将

$- 4$ 乘以

$1$ 。

$- 4 - 2 \cdot - 3 + 3 \cdot - 1$

解题步骤 1.5.1.2

将

$- 2$ 乘以

$- 3$ 。

$- 4 + 6 + 3 \cdot - 1$

解题步骤 1.5.1.3

将

$3$ 乘以

$- 1$ 。

$- 4 + 6 - 3$

解题步骤 1.5.2

将

$- 4$ 和

$6$ 相加。

$2 - 3$

解题步骤 1.5.3

从

$2$ 中减去

$3$ 。

$- 1$

解题步骤 2

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

解题步骤 3

Set up a

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

$[\begin{array}{c} 1 & 2 & 3 & 1 & 0 & 0 \\ 2 & 5 & 7 & 0 & 1 & 0 \\ 3 & 7 & 9 & 0 & 0 & 1 \end{array}]$

解题步骤 4

求行简化阶梯形矩阵。

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解题步骤 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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解题步骤 4.1.1

Perform the row operation

$R_{2} = R_{2} - 2 R_{1}$ to make the entry at

$2, 1$ a

$0$ .

$[\begin{array}{c} 1 & 2 & 3 & 1 & 0 & 0 \\ 2 - 2 \cdot 1 & 5 - 2 \cdot 2 & 7 - 2 \cdot 3 & 0 - 2 \cdot 1 & 1 - 2 \cdot 0 & 0 - 2 \cdot 0 \\ 3 & 7 & 9 & 0 & 0 & 1 \end{array}]$

解题步骤 4.1.2

化简

$R_{2}$ 。

$[\begin{array}{c} 1 & 2 & 3 & 1 & 0 & 0 \\ 0 & 1 & 1 & - 2 & 1 & 0 \\ 3 & 7 & 9 & 0 & 0 & 1 \end{array}]$

解题步骤 4.2

Perform the row operation

$R_{3} = R_{3} - 3 R_{1}$ to make the entry at

$3, 1$ a

$0$ .

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解题步骤 4.2.1

Perform the row operation

$R_{3} = R_{3} - 3 R_{1}$ to make the entry at

$3, 1$ a

$0$ .

$[\begin{array}{c} 1 & 2 & 3 & 1 & 0 & 0 \\ 0 & 1 & 1 & - 2 & 1 & 0 \\ 3 - 3 \cdot 1 & 7 - 3 \cdot 2 & 9 - 3 \cdot 3 & 0 - 3 \cdot 1 & 0 - 3 \cdot 0 & 1 - 3 \cdot 0 \end{array}]$

解题步骤 4.2.2

化简

$R_{3}$ 。

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

解题步骤 4.3

Perform the row operation

$R_{3} = R_{3} - R_{2}$ to make the entry at

$3, 2$ a

$0$ .

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解题步骤 4.3.1

Perform the row operation

$R_{3} = R_{3} - R_{2}$ to make the entry at

$3, 2$ a

$0$ .

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

解题步骤 4.3.2

化简

$R_{3}$ 。

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

解题步骤 4.4

Multiply each element of

$R_{3}$ by

$- 1$ to make the entry at

$3, 3$ a

$1$ .

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解题步骤 4.4.1

Multiply each element of

$R_{3}$ by

$- 1$ to make the entry at

$3, 3$ a

$1$ .

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

解题步骤 4.4.2

化简

$R_{3}$ 。

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

解题步骤 4.5

Perform the row operation

$R_{2} = R_{2} - R_{3}$ to make the entry at

$2, 3$ a

$0$ .

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解题步骤 4.5.1

Perform the row operation

$R_{2} = R_{2} - R_{3}$ to make the entry at

$2, 3$ a

$0$ .

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

解题步骤 4.5.2

化简

$R_{2}$ 。

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

解题步骤 4.6

Perform the row operation

$R_{1} = R_{1} - 3 R_{3}$ to make the entry at

$1, 3$ a

$0$ .

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解题步骤 4.6.1

Perform the row operation

$R_{1} = R_{1} - 3 R_{3}$ to make the entry at

$1, 3$ a

$0$ .

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

解题步骤 4.6.2

化简

$R_{1}$ 。

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

解题步骤 4.7

Perform the row operation

$R_{1} = R_{1} - 2 R_{2}$ to make the entry at

$1, 2$ a

$0$ .

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解题步骤 4.7.1

Perform the row operation

$R_{1} = R_{1} - 2 R_{2}$ to make the entry at

$1, 2$ a

$0$ .

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

解题步骤 4.7.2

化简

$R_{1}$ 。

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

解题步骤 5

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

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

线性代数 示例

线性代数示例