Find the Rank

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

Step 1

Find the reduced row echelon form.

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Step 1.1

Swap $R_{2}$ with $R_{1}$ to put a nonzero entry at $1, 1$ .

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

Step 1.2

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

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Step 1.2.1

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

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

Step 1.2.2

Simplify $R_{1}$ .

$[\begin{array}{c} 1 & 0 & - 1 & - 6 \\ 0 & 1 & 0 & 2 \end{array}]$

Step 2

The pivot positions are the locations with the leading $1$ in each row. The pivot columns are the columns that have a pivot position.

Pivot Positions: $a_{11}$ and $a_{22}$

Pivot Columns: $1$ and $2$

Step 3

The rank is the number of pivot columns.

$2$

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