Finite Math Examples

$x + 2 y = 4$ , $2 x + 6 y = 5$

Step 1

Represent the system of equations in matrix format.

$[\begin{array}{c} 1 & 2 \\ 2 & 6 \end{array}] [\begin{array}{c} x \\ y \end{array}] = [\begin{array}{c} 4 \\ 5 \end{array}]$

Step 2

Find the determinant of the coefficient matrix $[\begin{array}{c} 1 & 2 \\ 2 & 6 \end{array}]$ .

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Step 2.1

Write $[\begin{array}{c} 1 & 2 \\ 2 & 6 \end{array}]$ in determinant notation.

$| \begin{array}{c} 1 & 2 \\ 2 & 6 \end{array} |$

Step 2.2

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

$1 \cdot 6 - 2 \cdot 2$

Step 2.3

Simplify the determinant.

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Step 2.3.1

Simplify each term.

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Step 2.3.1.1

Multiply $6$ by $1$ .

$6 - 2 \cdot 2$

Step 2.3.1.2

Multiply $- 2$ by $2$ .

$6 - 4$

Step 2.3.2

Subtract $4$ from $6$ .

$2$

$D = 2$

Step 3

Since the determinant is not $0$ , the system can be solved using Cramer's Rule.

Step 4

Find the value of $x$ by Cramer's Rule, which states that $x = \frac{D_{x}}{D}$ .

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Step 4.1

Replace column $1$ of the coefficient matrix that corresponds to the $x$ -coefficients of the system with $[\begin{array}{c} 4 \\ 5 \end{array}]$ .

$| \begin{array}{c} 4 & 2 \\ 5 & 6 \end{array} |$

Step 4.2

Find the determinant.

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Step 4.2.1

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

$4 \cdot 6 - 5 \cdot 2$

Step 4.2.2

Simplify the determinant.

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Step 4.2.2.1

Simplify each term.

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Step 4.2.2.1.1

Multiply $4$ by $6$ .

$24 - 5 \cdot 2$

Step 4.2.2.1.2

Multiply $- 5$ by $2$ .

$24 - 10$

Step 4.2.2.2

Subtract $10$ from $24$ .

$14$

$D_{x} = 14$

Step 4.3

Use the formula to solve for $x$ .

$x = \frac{D_{x}}{D}$

Step 4.4

Substitute $2$ for $D$ and $14$ for $D_{x}$ in the formula.

$x = \frac{14}{2}$

Step 4.5

Divide $14$ by $2$ .

$x = 7$

Step 5

Find the value of $y$ by Cramer's Rule, which states that $y = \frac{D_{y}}{D}$ .

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Step 5.1

Replace column $2$ of the coefficient matrix that corresponds to the $y$ -coefficients of the system with $[\begin{array}{c} 4 \\ 5 \end{array}]$ .

$| \begin{array}{c} 1 & 4 \\ 2 & 5 \end{array} |$

Step 5.2

Find the determinant.

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Step 5.2.1

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

$1 \cdot 5 - 2 \cdot 4$

Step 5.2.2

Simplify the determinant.

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Step 5.2.2.1

Simplify each term.

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Step 5.2.2.1.1

Multiply $5$ by $1$ .

$5 - 2 \cdot 4$

Step 5.2.2.1.2

Multiply $- 2$ by $4$ .

$5 - 8$

Step 5.2.2.2

Subtract $8$ from $5$ .

$- 3$

$D_{y} = - 3$

Step 5.3

Use the formula to solve for $y$ .

$y = \frac{D_{y}}{D}$

Step 5.4

Substitute $2$ for $D$ and $- 3$ for $D_{y}$ in the formula.

$y = \frac{- 3}{2}$

Step 5.5

Move the negative in front of the fraction.

$y = - \frac{3}{2}$

Step 6

List the solution to the system of equations.

$x = 7$

$y = - \frac{3}{2}$