Find the Inverse [[8,7],[9,8]]

$[\begin{array}{c} 8 & 7 \\ 9 & 8 \end{array}]$

Step 1

The inverse of a $2 \times 2$ matrix can be found using the formula $\frac{1}{a d - b c} [\begin{array}{c} d & - b \\ - c & a \end{array}]$ where $a d - b c$ is the determinant.

Step 2

Find the determinant.

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

$8 \cdot 8 - 9 \cdot 7$

Simplify the determinant.

Simplify each term.

Multiply $8$ by $8$ .

$64 - 9 \cdot 7$

Multiply $- 9$ by $7$ .

$64 - 63$

Subtract $63$ from $64$ .

$1$

Step 3

Substitute the known values into the formula for the inverse.

$\frac{1}{1} [\begin{array}{c} 8 & - 7 \\ - 9 & 8 \end{array}]$

Step 4

Divide $1$ by $1$ .

$1 [\begin{array}{c} 8 & - 7 \\ - 9 & 8 \end{array}]$

Step 5

Multiply $1$ by each element of the matrix.

$[\begin{array}{c} 1 \cdot 8 & 1 \cdot - 7 \\ 1 \cdot - 9 & 1 \cdot 8 \end{array}]$

Step 6

Simplify each element in the matrix.

Multiply $8$ by $1$ .

$[\begin{array}{c} 8 & 1 \cdot - 7 \\ 1 \cdot - 9 & 1 \cdot 8 \end{array}]$

Multiply $- 7$ by $1$ .

$[\begin{array}{c} 8 & - 7 \\ 1 \cdot - 9 & 1 \cdot 8 \end{array}]$

Multiply $- 9$ by $1$ .

$[\begin{array}{c} 8 & - 7 \\ - 9 & 1 \cdot 8 \end{array}]$

Multiply $8$ by $1$ .

$[\begin{array}{c} 8 & - 7 \\ - 9 & 8 \end{array}]$

Find the Inverse [[8,7],[9,8]]

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