Solve {l}{10x=-8y+36}{-10=3y-8x}

$$\left. \begin{array} { l } { 10 x = - 8 y + 36 } \\ { - 10 = 3 y - 8 x } \end{array} \right.$$

Solve for x, y

$$x=2$$

$$y=2$$

Steps Using Substitution

Consider the first equation. Add 8y to both sides.

$$10x+8y=36$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$3y-8x=-10$$

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.

$$10x+8y=36,-8x+3y=-10$$

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

$$10x+8y=36$$

Subtract 8y from both sides of the equation.

$$10x=-8y+36$$

Divide both sides by 10.

$$x=\frac{1}{10}\left(-8y+36\right)$$

Multiply \frac{1}{10} times -8y+36.

$$x=-\frac{4}{5}y+\frac{18}{5}$$

Substitute \frac{-4y+18}{5} for x in the other equation, -8x+3y=-10.

$$-8\left(-\frac{4}{5}y+\frac{18}{5}\right)+3y=-10$$

Multiply -8 times \frac{-4y+18}{5}.

$$\frac{32}{5}y-\frac{144}{5}+3y=-10$$

Add \frac{32y}{5} to 3y.

$$\frac{47}{5}y-\frac{144}{5}=-10$$

Add \frac{144}{5} to both sides of the equation.

$$\frac{47}{5}y=\frac{94}{5}$$

Divide both sides of the equation by \frac{47}{5}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=2$$

Substitute 2 for y in x=-\frac{4}{5}y+\frac{18}{5}. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=-\frac{4}{5}\times 2+\frac{18}{5}$$

Multiply -\frac{4}{5} times 2.

$$x=\frac{-8+18}{5}$$

Add \frac{18}{5} to -\frac{8}{5} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x=2$$

The system is now solved.

$$x=2,y=2$$

Steps Using Matrices

Consider the first equation. Add 8y to both sides.

$$10x+8y=36$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$3y-8x=-10$$

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

$$10x+8y=36,-8x+3y=-10$$

Write the equations in matrix form.

$$\left(\begin{matrix}10&8\\-8&3\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}36\\-10\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}10&8\\-8&3\end{matrix}\right).

$$inverse(\left(\begin{matrix}10&8\\-8&3\end{matrix}\right))\left(\begin{matrix}10&8\\-8&3\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}10&8\\-8&3\end{matrix}\right))\left(\begin{matrix}36\\-10\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}10&8\\-8&3\end{matrix}\right))\left(\begin{matrix}36\\-10\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}10&8\\-8&3\end{matrix}\right))\left(\begin{matrix}36\\-10\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{3}{10\times 3-8\left(-8\right)}&-\frac{8}{10\times 3-8\left(-8\right)}\\-\frac{-8}{10\times 3-8\left(-8\right)}&\frac{10}{10\times 3-8\left(-8\right)}\end{matrix}\right)\left(\begin{matrix}36\\-10\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{3}{94}&-\frac{4}{47}\\\frac{4}{47}&\frac{5}{47}\end{matrix}\right)\left(\begin{matrix}36\\-10\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{3}{94}\times 36-\frac{4}{47}\left(-10\right)\\\frac{4}{47}\times 36+\frac{5}{47}\left(-10\right)\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}2\\2\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=2,y=2$$

Steps Using Elimination

Consider the first equation. Add 8y to both sides.

$$10x+8y=36$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$3y-8x=-10$$

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.

$$10x+8y=36,-8x+3y=-10$$

To make 10x and -8x equal, multiply all terms on each side of the first equation by -8 and all terms on each side of the second by 10.

$$-8\times 10x-8\times 8y=-8\times 36,10\left(-8\right)x+10\times 3y=10\left(-10\right)$$

Simplify.

$$-80x-64y=-288,-80x+30y=-100$$

Subtract -80x+30y=-100 from -80x-64y=-288 by subtracting like terms on each side of the equal sign.

$$-80x+80x-64y-30y=-288+100$$

Add -80x to 80x. Terms -80x and 80x cancel out, leaving an equation with only one variable that can be solved.

$$-64y-30y=-288+100$$

Add -64y to -30y.

$$-94y=-288+100$$

Add -288 to 100.

$$-94y=-188$$

Divide both sides by -94.

$$y=2$$

Substitute 2 for y in -8x+3y=-10. Because the resulting equation contains only one variable, you can solve for x directly.

$$-8x+3\times 2=-10$$

Multiply 3 times 2.

$$-8x+6=-10$$

Subtract 6 from both sides of the equation.

$$-8x=-16$$

Divide both sides by -8.

$$x=2$$

The system is now solved.

$$x=2,y=2$$