Examples

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

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

Step 1

Find the reduced row echelon form.

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Step 1.1

Multiply each element of

R_{1}

$R_{1}$ by

\frac{1}{2}

$\frac{1}{2}$ to make the entry at

1, 1

$1, 1$ a

1

$1$ .

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Step 1.1.1

Multiply each element of

R_{1}

$R_{1}$ by

\frac{1}{2}

$\frac{1}{2}$ to make the entry at

1, 1

$1, 1$ a

1

$1$ .

[\begin{array}{c} \frac{2}{2} & \frac{- 2}{2} & \frac{9}{2} \\ 1 & 2 & 3 \end{array}]

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

Step 1.1.2

Simplify

R_{1}

$R_{1}$ .

[\begin{array}{c} 1 & - 1 & \frac{9}{2} \\ 1 & 2 & 3 \end{array}]

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

[\begin{array}{c} 1 & - 1 & \frac{9}{2} \\ 1 & 2 & 3 \end{array}]

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

Step 1.2

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 1.2.1

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

$0$ .

[\begin{array}{c} 1 & - 1 & \frac{9}{2} \\ 1 - 1 & 2 + 1 & 3 - \frac{9}{2} \end{array}]

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

Step 1.2.2

Simplify

R_{2}

$R_{2}$ .

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

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

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

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

Step 1.3

Multiply each element of

R_{2}

$R_{2}$ by

\frac{1}{3}

$\frac{1}{3}$ to make the entry at

2, 2

$2, 2$ a

1

$1$ .

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Step 1.3.1

Multiply each element of

R_{2}

$R_{2}$ by

\frac{1}{3}

$\frac{1}{3}$ to make the entry at

2, 2

$2, 2$ a

1

$1$ .

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

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

Step 1.3.2

Simplify

R_{2}

$R_{2}$ .

[\begin{array}{c} 1 & - 1 & \frac{9}{2} \\ 0 & 1 & - \frac{1}{2} \end{array}]

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

[\begin{array}{c} 1 & - 1 & \frac{9}{2} \\ 0 & 1 & - \frac{1}{2} \end{array}]

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

Step 1.4

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 1.4.1

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 \cdot 1 & \frac{9}{2} - \frac{1}{2} \\ 0 & 1 & - \frac{1}{2} \end{array}]

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

Step 1.4.2

Simplify

R_{1}

$R_{1}$ .

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

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

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

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

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

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

Step 2

The pivot positions are the locations with the leading

1

$1$ in each row. The pivot columns are the columns that have a pivot position.

Pivot Positions:

a_{11}

$a_{11}$ and

a_{22}

$a_{22}$

Pivot Columns:

1

$1$ and

2

$2$

Step 3

The rank is the number of pivot columns.

2

$2$

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