Solve {l}{13x+11y=617}{8x+11y=477}

$$\left. \begin{array} { l } { 13 x + 11 y = 617 } \\ { 8 x + 11 y = 477 } \end{array} \right.$$

Solve for x, y

$$x=28$$

$$y=23$$

Steps Using Substitution

To solve a pair of equations using substitution, first solve one of the equations for one of the variables. Then substitute the result for that variable in the other equation.

$$13x+11y=617,8x+11y=477$$

Choose one of the equations and solve it for x by isolating x on the left hand side of the equal sign.

$$13x+11y=617$$

Subtract 11y from both sides of the equation.

$$13x=-11y+617$$

Divide both sides by 13.

$$x=\frac{1}{13}\left(-11y+617\right)$$

Multiply \frac{1}{13} times -11y+617.

$$x=-\frac{11}{13}y+\frac{617}{13}$$

Substitute \frac{-11y+617}{13} for x in the other equation, 8x+11y=477.

$$8\left(-\frac{11}{13}y+\frac{617}{13}\right)+11y=477$$

Multiply 8 times \frac{-11y+617}{13}.

$$-\frac{88}{13}y+\frac{4936}{13}+11y=477$$

Add -\frac{88y}{13} to 11y.

$$\frac{55}{13}y+\frac{4936}{13}=477$$

Subtract \frac{4936}{13} from both sides of the equation.

$$\frac{55}{13}y=\frac{1265}{13}$$

Divide both sides of the equation by \frac{55}{13}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=23$$

Substitute 23 for y in x=-\frac{11}{13}y+\frac{617}{13}. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=-\frac{11}{13}\times 23+\frac{617}{13}$$

Multiply -\frac{11}{13} times 23.

$$x=\frac{-253+617}{13}$$

Add \frac{617}{13} to -\frac{253}{13} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x=28$$

The system is now solved.

$$x=28,y=23$$

Steps Using Matrices

Put the equations in standard form and then use matrices to solve the system of equations.

$$13x+11y=617,8x+11y=477$$

Write the equations in matrix form.

$$\left(\begin{matrix}13&11\\8&11\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}617\\477\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}13&11\\8&11\end{matrix}\right).

$$inverse(\left(\begin{matrix}13&11\\8&11\end{matrix}\right))\left(\begin{matrix}13&11\\8&11\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}13&11\\8&11\end{matrix}\right))\left(\begin{matrix}617\\477\end{matrix}\right)$$

The product of a matrix and its inverse is the identity matrix.

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}13&11\\8&11\end{matrix}\right))\left(\begin{matrix}617\\477\end{matrix}\right)$$

Multiply the matrices on the left hand side of the equal sign.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}13&11\\8&11\end{matrix}\right))\left(\begin{matrix}617\\477\end{matrix}\right)$$

For the 2\times 2 matrix \left(\begin{matrix}a&b\\c&d\end{matrix}\right), the inverse matrix is \left(\begin{matrix}\frac{d}{ad-bc}&\frac{-b}{ad-bc}\\\frac{-c}{ad-bc}&\frac{a}{ad-bc}\end{matrix}\right), so the matrix equation can be rewritten as a matrix multiplication problem.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{11}{13\times 11-11\times 8}&-\frac{11}{13\times 11-11\times 8}\\-\frac{8}{13\times 11-11\times 8}&\frac{13}{13\times 11-11\times 8}\end{matrix}\right)\left(\begin{matrix}617\\477\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{1}{5}&-\frac{1}{5}\\-\frac{8}{55}&\frac{13}{55}\end{matrix}\right)\left(\begin{matrix}617\\477\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{1}{5}\times 617-\frac{1}{5}\times 477\\-\frac{8}{55}\times 617+\frac{13}{55}\times 477\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}28\\23\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=28,y=23$$

Steps Using Elimination

In order to solve by elimination, coefficients of one of the variables must be the same in both equations so that the variable will cancel out when one equation is subtracted from the other.

$$13x+11y=617,8x+11y=477$$

Subtract 8x+11y=477 from 13x+11y=617 by subtracting like terms on each side of the equal sign.

$$13x-8x+11y-11y=617-477$$

Add 11y to -11y. Terms 11y and -11y cancel out, leaving an equation with only one variable that can be solved.

$$13x-8x=617-477$$

Add 13x to -8x.

$$5x=617-477$$

Add 617 to -477.

$$5x=140$$

Divide both sides by 5.

$$x=28$$

Substitute 28 for x in 8x+11y=477. Because the resulting equation contains only one variable, you can solve for y directly.

$$8\times 28+11y=477$$

Multiply 8 times 28.

$$224+11y=477$$

Subtract 224 from both sides of the equation.

$$11y=253$$

Divide both sides by 11.

$$y=23$$

The system is now solved.

$$x=28,y=23$$