Solve {l}{234x+180y=117}{180x+234y=104}

$$\left\{ \begin{array} { l } { 234 x + 180 y = 117 } \\ { 180 x + 234 y = 104 } \end{array} \right.$$

Solve for x, y

$$x=\frac{481}{1242}\approx 0.387278583$$

$$y=\frac{91}{621}\approx 0.146537842$$

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.

$$234x+180y=117,180x+234y=104$$

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

$$234x+180y=117$$

Subtract 180y from both sides of the equation.

$$234x=-180y+117$$

Divide both sides by 234.

$$x=\frac{1}{234}\left(-180y+117\right)$$

Multiply \frac{1}{234} times -180y+117.

$$x=-\frac{10}{13}y+\frac{1}{2}$$

Substitute -\frac{10y}{13}+\frac{1}{2} for x in the other equation, 180x+234y=104.

$$180\left(-\frac{10}{13}y+\frac{1}{2}\right)+234y=104$$

Multiply 180 times -\frac{10y}{13}+\frac{1}{2}.

$$-\frac{1800}{13}y+90+234y=104$$

Add -\frac{1800y}{13} to 234y.

$$\frac{1242}{13}y+90=104$$

Subtract 90 from both sides of the equation.

$$\frac{1242}{13}y=14$$

Divide both sides of the equation by \frac{1242}{13}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=\frac{91}{621}$$

Substitute \frac{91}{621} for y in x=-\frac{10}{13}y+\frac{1}{2}. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=-\frac{10}{13}\times \frac{91}{621}+\frac{1}{2}$$

Multiply -\frac{10}{13} times \frac{91}{621} by multiplying numerator times numerator and denominator times denominator. Then reduce the fraction to lowest terms if possible.

$$x=-\frac{70}{621}+\frac{1}{2}$$

Add \frac{1}{2} to -\frac{70}{621} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x=\frac{481}{1242}$$

The system is now solved.

$$x=\frac{481}{1242},y=\frac{91}{621}$$

Steps Using Matrices

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

$$234x+180y=117,180x+234y=104$$

Write the equations in matrix form.

$$\left(\begin{matrix}234&180\\180&234\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}117\\104\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}234&180\\180&234\end{matrix}\right).

$$inverse(\left(\begin{matrix}234&180\\180&234\end{matrix}\right))\left(\begin{matrix}234&180\\180&234\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}234&180\\180&234\end{matrix}\right))\left(\begin{matrix}117\\104\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}234&180\\180&234\end{matrix}\right))\left(\begin{matrix}117\\104\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}234&180\\180&234\end{matrix}\right))\left(\begin{matrix}117\\104\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{234}{234\times 234-180\times 180}&-\frac{180}{234\times 234-180\times 180}\\-\frac{180}{234\times 234-180\times 180}&\frac{234}{234\times 234-180\times 180}\end{matrix}\right)\left(\begin{matrix}117\\104\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{13}{1242}&-\frac{5}{621}\\-\frac{5}{621}&\frac{13}{1242}\end{matrix}\right)\left(\begin{matrix}117\\104\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{13}{1242}\times 117-\frac{5}{621}\times 104\\-\frac{5}{621}\times 117+\frac{13}{1242}\times 104\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{481}{1242}\\\frac{91}{621}\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=\frac{481}{1242},y=\frac{91}{621}$$

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.

$$234x+180y=117,180x+234y=104$$

To make 234x and 180x equal, multiply all terms on each side of the first equation by 180 and all terms on each side of the second by 234.

$$180\times 234x+180\times 180y=180\times 117,234\times 180x+234\times 234y=234\times 104$$

Simplify.

$$42120x+32400y=21060,42120x+54756y=24336$$

Subtract 42120x+54756y=24336 from 42120x+32400y=21060 by subtracting like terms on each side of the equal sign.

$$42120x-42120x+32400y-54756y=21060-24336$$

Add 42120x to -42120x. Terms 42120x and -42120x cancel out, leaving an equation with only one variable that can be solved.

$$32400y-54756y=21060-24336$$

Add 32400y to -54756y.

$$-22356y=21060-24336$$

Add 21060 to -24336.

$$-22356y=-3276$$

Divide both sides by -22356.

$$y=\frac{91}{621}$$

Substitute \frac{91}{621} for y in 180x+234y=104. Because the resulting equation contains only one variable, you can solve for x directly.

$$180x+234\times \frac{91}{621}=104$$

Multiply 234 times \frac{91}{621}.

$$180x+\frac{2366}{69}=104$$

Subtract \frac{2366}{69} from both sides of the equation.

$$180x=\frac{4810}{69}$$

Divide both sides by 180.

$$x=\frac{481}{1242}$$

The system is now solved.

$$x=\frac{481}{1242},y=\frac{91}{621}$$