Linear Algebra Examples

$[\begin{array}{c} x & - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x & - \frac{1}{6} \\ - \frac{1}{6} & - \frac{1}{6} & x \end{array}]$

Step 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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Step 1.1

Consider the corresponding sign chart.

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

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

$| \begin{array}{c} x & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} |$

Step 1.4

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

$x | \begin{array}{c} x & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} |$

Step 1.5

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

$| \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} |$

Step 1.6

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

$\frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} |$

Step 1.7

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

$| \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 1.8

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

$- \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 1.9

Add the terms together.

$x | \begin{array}{c} x & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | + \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 2

Evaluate $| \begin{array}{c} x & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} |$ .

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Step 2.1

The determinant of a $2 \times 2$ matrix can be found using the formula $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$x (x \cdot x - (- \frac{1}{6} (- \frac{1}{6}))) + \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 2.2

Simplify each term.

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Step 2.2.1

Multiply $x$ by $x$ .

$x (x^{2} - (- \frac{1}{6} (- \frac{1}{6}))) + \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 2.2.2

Multiply $- \frac{1}{6} (- \frac{1}{6})$ .

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Step 2.2.2.1

Multiply $- 1$ by $- 1$ .

$x (x^{2} - (1 (\frac{1}{6}) \frac{1}{6})) + \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 2.2.2.2

Multiply $\frac{1}{6}$ by $1$ .

$x (x^{2} - (\frac{1}{6} \cdot \frac{1}{6})) + \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 2.2.2.3

Multiply $\frac{1}{6}$ by $\frac{1}{6}$ .

$x (x^{2} - \frac{1}{6 \cdot 6}) + \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 2.2.2.4

Multiply $6$ by $6$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} | - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 3

Evaluate $| \begin{array}{c} - \frac{1}{6} & - \frac{1}{6} \\ - \frac{1}{6} & x \end{array} |$ .

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Step 3.1

The determinant of a $2 \times 2$ matrix can be found using the formula $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{1}{6} x - (- \frac{1}{6} (- \frac{1}{6}))) - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 3.2

Simplify each term.

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Step 3.2.1

Combine $x$ and $\frac{1}{6}$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - (- \frac{1}{6} (- \frac{1}{6}))) - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 3.2.2

Multiply $- \frac{1}{6} (- \frac{1}{6})$ .

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Step 3.2.2.1

Multiply $- 1$ by $- 1$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - (1 (\frac{1}{6}) \frac{1}{6})) - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 3.2.2.2

Multiply $\frac{1}{6}$ by $1$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - (\frac{1}{6} \cdot \frac{1}{6})) - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 3.2.2.3

Multiply $\frac{1}{6}$ by $\frac{1}{6}$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{6 \cdot 6}) - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 3.2.2.4

Multiply $6$ by $6$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} | \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$

Step 4

Evaluate $| \begin{array}{c} - \frac{1}{6} & x \\ - \frac{1}{6} & - \frac{1}{6} \end{array} |$ .

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Step 4.1

The determinant of a $2 \times 2$ matrix can be found using the formula $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (- \frac{1}{6} (- \frac{1}{6}) - (- \frac{1}{6} x))$

Step 4.2

Simplify each term.

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Step 4.2.1

Multiply $- \frac{1}{6} (- \frac{1}{6})$ .

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Step 4.2.1.1

Multiply $- 1$ by $- 1$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (1 (\frac{1}{6}) \frac{1}{6} - (- \frac{1}{6} x))$

Step 4.2.1.2

Multiply $\frac{1}{6}$ by $1$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{6} \cdot \frac{1}{6} - (- \frac{1}{6} x))$

Step 4.2.1.3

Multiply $\frac{1}{6}$ by $\frac{1}{6}$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{6 \cdot 6} - (- \frac{1}{6} x))$

Step 4.2.1.4

Multiply $6$ by $6$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} - (- \frac{1}{6} x))$

Step 4.2.2

Combine $x$ and $\frac{1}{6}$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} - - \frac{x}{6})$

Step 4.2.3

Multiply $- - \frac{x}{6}$ .

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Step 4.2.3.1

Multiply $- 1$ by $- 1$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + 1 \frac{x}{6})$

Step 4.2.3.2

Multiply $\frac{x}{6}$ by $1$ .

$x (x^{2} - \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5

Simplify the determinant.

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Step 5.1

Simplify each term.

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Step 5.1.1

Apply the distributive property.

$x \cdot x^{2} + x (- \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.2

Multiply $x$ by $x^{2}$ by adding the exponents.

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Step 5.1.2.1

Multiply $x$ by $x^{2}$ .

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Step 5.1.2.1.1

Raise $x$ to the power of $1$ .

$x^{1} x^{2} + x (- \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.2.1.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$x^{1 + 2} + x (- \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.2.2

Add $1$ and $2$ .

$x^{3} + x (- \frac{1}{36}) + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.3

Combine $x$ and $\frac{1}{36}$ .

$x^{3} - \frac{x}{36} + \frac{1}{6} (- \frac{x}{6} - \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.4

Apply the distributive property.

$x^{3} - \frac{x}{36} + \frac{1}{6} (- \frac{x}{6}) + \frac{1}{6} (- \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.5

Multiply $\frac{1}{6} (- \frac{x}{6})$ .

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Step 5.1.5.1

Multiply $\frac{1}{6}$ by $\frac{x}{6}$ .

$x^{3} - \frac{x}{36} - \frac{x}{6 \cdot 6} + \frac{1}{6} (- \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.5.2

Multiply $6$ by $6$ .

$x^{3} - \frac{x}{36} - \frac{x}{36} + \frac{1}{6} (- \frac{1}{36}) - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.6

Multiply $\frac{1}{6} (- \frac{1}{36})$ .

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Step 5.1.6.1

Multiply $\frac{1}{6}$ by $\frac{1}{36}$ .

$x^{3} - \frac{x}{36} - \frac{x}{36} - \frac{1}{6 \cdot 36} - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.6.2

Multiply $6$ by $36$ .

$x^{3} - \frac{x}{36} - \frac{x}{36} - \frac{1}{216} - \frac{1}{6} (\frac{1}{36} + \frac{x}{6})$

Step 5.1.7

Apply the distributive property.

$x^{3} - \frac{x}{36} - \frac{x}{36} - \frac{1}{216} - \frac{1}{6} \cdot \frac{1}{36} - \frac{1}{6} \cdot \frac{x}{6}$

Step 5.1.8

Multiply $- \frac{1}{6} \cdot \frac{1}{36}$ .

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Step 5.1.8.1

Multiply $\frac{1}{36}$ by $\frac{1}{6}$ .

$x^{3} - \frac{x}{36} - \frac{x}{36} - \frac{1}{216} - \frac{1}{36 \cdot 6} - \frac{1}{6} \cdot \frac{x}{6}$

Step 5.1.8.2

Multiply $36$ by $6$ .

$x^{3} - \frac{x}{36} - \frac{x}{36} - \frac{1}{216} - \frac{1}{216} - \frac{1}{6} \cdot \frac{x}{6}$

Step 5.1.9

Multiply $- \frac{1}{6} \cdot \frac{x}{6}$ .

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Step 5.1.9.1

Multiply $\frac{x}{6}$ by $\frac{1}{6}$ .

$x^{3} - \frac{x}{36} - \frac{x}{36} - \frac{1}{216} - \frac{1}{216} - \frac{x}{6 \cdot 6}$

Step 5.1.9.2

Multiply $6$ by $6$ .

$x^{3} - \frac{x}{36} - \frac{x}{36} - \frac{1}{216} - \frac{1}{216} - \frac{x}{36}$

Step 5.2

Combine the numerators over the common denominator.

$x^{3} + \frac{- x - x - x}{36} + \frac{- 1 - 1}{216}$

Step 5.3

Subtract $x$ from $- x$ .

$x^{3} + \frac{- 2 x - x}{36} + \frac{- 1 - 1}{216}$

Step 5.4

Subtract $x$ from $- 2 x$ .

$x^{3} + \frac{- 3 x}{36} + \frac{- 1 - 1}{216}$

Step 5.5

Subtract $1$ from $- 1$ .

$x^{3} + \frac{- 3 x}{36} + \frac{- 2}{216}$

Step 5.6

Simplify each term.

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Step 5.6.1

Cancel the common factor of $- 3$ and $36$ .

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Step 5.6.1.1

Factor $3$ out of $- 3 x$ .

$x^{3} + \frac{3 (- x)}{36} + \frac{- 2}{216}$

Step 5.6.1.2

Cancel the common factors.

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Step 5.6.1.2.1

Factor $3$ out of $36$ .

$x^{3} + \frac{3 (- x)}{3 (12)} + \frac{- 2}{216}$

Step 5.6.1.2.2

Cancel the common factor.

$x^{3} + \frac{3 (- x)}{3 \cdot 12} + \frac{- 2}{216}$

Step 5.6.1.2.3

Rewrite the expression.

$x^{3} + \frac{- x}{12} + \frac{- 2}{216}$

Step 5.6.2

Move the negative in front of the fraction.

$x^{3} - \frac{x}{12} + \frac{- 2}{216}$

Step 5.6.3

Cancel the common factor of $- 2$ and $216$ .

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Step 5.6.3.1

Factor $2$ out of $- 2$ .

$x^{3} - \frac{x}{12} + \frac{2 (- 1)}{216}$

Step 5.6.3.2

Cancel the common factors.

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Step 5.6.3.2.1

Factor $2$ out of $216$ .

$x^{3} - \frac{x}{12} + \frac{2 \cdot - 1}{2 \cdot 108}$

Step 5.6.3.2.2

Cancel the common factor.

$x^{3} - \frac{x}{12} + \frac{2 \cdot - 1}{2 \cdot 108}$

Step 5.6.3.2.3

Rewrite the expression.

$x^{3} - \frac{x}{12} + \frac{- 1}{108}$

Step 5.6.4

Move the negative in front of the fraction.

$x^{3} - \frac{x}{12} - \frac{1}{108}$