Linear Algebra Examples

x + y + 4 z = 2

$x + y + 4 z = 2$ ,

x + 2 y - 4 z = 1

$x + 2 y - 4 z = 1$ ,

3 x + 8 y + k z = 2

$3 x + 8 y + k z = 2$

Step 1

Write the system of equations in matrix form.

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 1 & 2 & - 4 & 1 \\ 3 & 8 & k & 2 \end{array}]

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

Step 2

Find the reduced row echelon form.

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Step 2.1

Perform the row operation

R_{2} = R_{2} - R_{1}

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

2, 1

$2, 1$ a

0

$0$ .

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Step 2.1.1

Perform the row operation

R_{2} = R_{2} - R_{1}

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

2, 1

$2, 1$ a

0

$0$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 1 - 1 & 2 - 1 & - 4 - 4 & 1 - 2 \\ 3 & 8 & k & 2 \end{array}]

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

Step 2.1.2

Simplify

R_{2}

$R_{2}$ .

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

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

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

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

Step 2.2

Perform the row operation

R_{3} = R_{3} - 3 R_{1}

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

3, 1

$3, 1$ a

0

$0$ .

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Step 2.2.1

Perform the row operation

R_{3} = R_{3} - 3 R_{1}

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

3, 1

$3, 1$ a

0

$0$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 3 - 3 \cdot 1 & 8 - 3 \cdot 1 & k - 3 \cdot 4 & 2 - 3 \cdot 2 \end{array}]

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

Step 2.2.2

Simplify

R_{3}

$R_{3}$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 5 & k - 12 & - 4 \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 5 & k - 12 & - 4 \end{array}]$

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 5 & k - 12 & - 4 \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 5 & k - 12 & - 4 \end{array}]$

Step 2.3

Perform the row operation

R_{3} = R_{3} - 5 R_{2}

$R_{3} = R_{3} - 5 R_{2}$ to make the entry at

3, 2

$3, 2$ a

0

$0$ .

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Step 2.3.1

Perform the row operation

R_{3} = R_{3} - 5 R_{2}

$R_{3} = R_{3} - 5 R_{2}$ to make the entry at

3, 2

$3, 2$ a

0

$0$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 - 5 \cdot 0 & 5 - 5 \cdot 1 & k - 12 - 5 \cdot - 8 & - 4 - 5 \cdot - 1 \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 - 5 \cdot 0 & 5 - 5 \cdot 1 & k - 12 - 5 \cdot - 8 & - 4 - 5 \cdot - 1 \end{array}]$

Step 2.3.2

Simplify

R_{3}

$R_{3}$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & k + 28 & 1 \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & k + 28 & 1 \end{array}]$

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & k + 28 & 1 \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & k + 28 & 1 \end{array}]$

Step 2.4

Multiply each element of

R_{3}

$R_{3}$ by

\frac{1}{k + 28}

$\frac{1}{k + 28}$ to make the entry at

3, 3

$3, 3$ a

1

$1$ .

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Step 2.4.1

Multiply each element of

R_{3}

$R_{3}$ by

\frac{1}{k + 28}

$\frac{1}{k + 28}$ to make the entry at

3, 3

$3, 3$ a

1

$1$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ \frac{0}{k + 28} & \frac{0}{k + 28} & \frac{k + 28}{k + 28} & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ \frac{0}{k + 28} & \frac{0}{k + 28} & \frac{k + 28}{k + 28} & \frac{1}{k + 28} \end{array}]$

Step 2.4.2

Simplify

R_{3}

$R_{3}$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & - 8 & - 1 \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

Step 2.5

Perform the row operation

R_{2} = R_{2} + 8 R_{3}

$R_{2} = R_{2} + 8 R_{3}$ to make the entry at

2, 3

$2, 3$ a

0

$0$ .

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Step 2.5.1

Perform the row operation

R_{2} = R_{2} + 8 R_{3}

$R_{2} = R_{2} + 8 R_{3}$ to make the entry at

2, 3

$2, 3$ a

0

$0$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 + 8 \cdot 0 & 1 + 8 \cdot 0 & - 8 + 8 \cdot 1 & - 1 + 8 \frac{1}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 + 8 \cdot 0 & 1 + 8 \cdot 0 & - 8 + 8 \cdot 1 & - 1 + 8 \frac{1}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

Step 2.5.2

Simplify

R_{2}

$R_{2}$ .

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 4 & 2 \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

Step 2.6

Perform the row operation

R_{1} = R_{1} - 4 R_{3}

$R_{1} = R_{1} - 4 R_{3}$ to make the entry at

1, 3

$1, 3$ a

0

$0$ .

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Step 2.6.1

Perform the row operation

R_{1} = R_{1} - 4 R_{3}

$R_{1} = R_{1} - 4 R_{3}$ to make the entry at

1, 3

$1, 3$ a

0

$0$ .

[\begin{array}{c} 1 - 4 \cdot 0 & 1 - 4 \cdot 0 & 4 - 4 \cdot 1 & 2 - 4 \frac{1}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 - 4 \cdot 0 & 1 - 4 \cdot 0 & 4 - 4 \cdot 1 & 2 - 4 \frac{1}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

Step 2.6.2

Simplify

R_{1}

$R_{1}$ .

[\begin{array}{c} 1 & 1 & 0 & \frac{2 (k + 26)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 0 & \frac{2 (k + 26)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

[\begin{array}{c} 1 & 1 & 0 & \frac{2 (k + 26)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 1 & 0 & \frac{2 (k + 26)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

Step 2.7

Perform the row operation

R_{1} = R_{1} - R_{2}

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

1, 2

$1, 2$ a

0

$0$ .

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Step 2.7.1

Perform the row operation

R_{1} = R_{1} - R_{2}

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

1, 2

$1, 2$ a

0

$0$ .

[\begin{array}{c} 1 - 0 & 1 - 1 & 0 - 0 & \frac{2 (k + 26)}{k + 28} + \frac{k + 20}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 - 0 & 1 - 1 & 0 - 0 & \frac{2 (k + 26)}{k + 28} + \frac{k + 20}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

Step 2.7.2

Simplify

R_{1}

$R_{1}$ .

[\begin{array}{c} 1 & 0 & 0 & \frac{3 (k + 24)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 0 & 0 & \frac{3 (k + 24)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

[\begin{array}{c} 1 & 0 & 0 & \frac{3 (k + 24)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 0 & 0 & \frac{3 (k + 24)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

[\begin{array}{c} 1 & 0 & 0 & \frac{3 (k + 24)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]

$[\begin{array}{c} 1 & 0 & 0 & \frac{3 (k + 24)}{k + 28} \\ 0 & 1 & 0 & - \frac{k + 20}{k + 28} \\ 0 & 0 & 1 & \frac{1}{k + 28} \end{array}]$

Step 3

Since

\frac{1}{k + 28}

$\frac{1}{k + 28}$ is undefined when

k = - 28

$k = - 28$ , then

k = - 28

$k = - 28$ makes the system have no solution.

k = - 28

$k = - 28$

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