Solve {l}{7x-8/5y=0}{-150(7)(3,5)+4y-7x=0}

$$\left\{ \begin{array} { l } { 7 x - \frac { 8 } { 5 } y = 0 } \\ { - 150 ( 7 ) ( 3,5 ) + 4 y - 7 x = 0 } \end{array} \right.$$

Solve for x, y

$$x=350$$

$$y=1531,25$$

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.

$$7x-\frac{8}{5}y=0;-7x+4y-3675=0$$

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

$$7x-\frac{8}{5}y=0$$

Add \frac{8y}{5} to both sides of the equation.

$$7x=\frac{8}{5}y$$

Divide both sides by 7.

$$x=\frac{1}{7}\times \frac{8}{5}y$$

Multiply \frac{1}{7} times \frac{8y}{5}.

$$x=\frac{8}{35}y$$

Substitute \frac{8y}{35} for x in the other equation, -7x+4y-3675=0.

$$-7\times \frac{8}{35}y+4y-3675=0$$

Multiply -7 times \frac{8y}{35}.

$$-\frac{8}{5}y+4y-3675=0$$

Add -\frac{8y}{5} to 4y.

$$\frac{12}{5}y-3675=0$$

Add 3675 to both sides of the equation.

$$\frac{12}{5}y=3675$$

Divide both sides of the equation by \frac{12}{5}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=\frac{6125}{4}$$

Substitute \frac{6125}{4} for y in x=\frac{8}{35}y. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=\frac{8}{35}\times \frac{6125}{4}$$

Multiply \frac{8}{35} times \frac{6125}{4} by multiplying numerator times numerator and denominator times denominator. Then reduce the fraction to lowest terms if possible.

$$x=350$$

The system is now solved.

$$x=350;y=\frac{6125}{4}$$

Steps Using Matrices

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

$$7x-\frac{8}{5}y=0;-7x+4y-3675=0$$

Write the equations in matrix form.

$$\left(\begin{matrix}7&-\frac{8}{5}\\-7&4\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}0\\3675\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}7&-\frac{8}{5}\\-7&4\end{matrix}\right).

$$inverse(\left(\begin{matrix}7&-\frac{8}{5}\\-7&4\end{matrix}\right))\left(\begin{matrix}7&-\frac{8}{5}\\-7&4\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}7&-\frac{8}{5}\\-7&4\end{matrix}\right))\left(\begin{matrix}0\\3675\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}7&-\frac{8}{5}\\-7&4\end{matrix}\right))\left(\begin{matrix}0\\3675\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}7&-\frac{8}{5}\\-7&4\end{matrix}\right))\left(\begin{matrix}0\\3675\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{4}{7\times 4-\left(-\frac{8}{5}\left(-7\right)\right)}&-\frac{-\frac{8}{5}}{7\times 4-\left(-\frac{8}{5}\left(-7\right)\right)}\\-\frac{-7}{7\times 4-\left(-\frac{8}{5}\left(-7\right)\right)}&\frac{7}{7\times 4-\left(-\frac{8}{5}\left(-7\right)\right)}\end{matrix}\right)\left(\begin{matrix}0\\3675\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{5}{21}&\frac{2}{21}\\\frac{5}{12}&\frac{5}{12}\end{matrix}\right)\left(\begin{matrix}0\\3675\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{2}{21}\times 3675\\\frac{5}{12}\times 3675\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}350\\\frac{6125}{4}\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=350;y=\frac{6125}{4}$$

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.

$$7x-\frac{8}{5}y=0;-7x+4y-3675=0$$

To make 7x and -7x equal, multiply all terms on each side of the first equation by -7 and all terms on each side of the second by 7.

$$-7\times 7x-7\left(-\frac{8}{5}\right)y=0;7\left(-7\right)x+7\times 4y+7\left(-3675\right)=0$$

Simplify.

$$-49x+\frac{56}{5}y=0;-49x+28y-25725=0$$

Subtract -49x+28y-25725=0 from -49x+\frac{56}{5}y=0 by subtracting like terms on each side of the equal sign.

$$-49x+49x+\frac{56}{5}y-28y+25725=0$$

Add -49x to 49x. Terms -49x and 49x cancel out, leaving an equation with only one variable that can be solved.

$$\frac{56}{5}y-28y+25725=0$$

Add \frac{56y}{5} to -28y.

$$-\frac{84}{5}y+25725=0$$

Subtract 25725 from both sides of the equation.

$$-\frac{84}{5}y=-25725$$

Divide both sides of the equation by -\frac{84}{5}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=\frac{6125}{4}$$

Substitute \frac{6125}{4} for y in -7x+4y-3675=0. Because the resulting equation contains only one variable, you can solve for x directly.

$$-7x+4\times \frac{6125}{4}-3675=0$$

Multiply 4 times \frac{6125}{4}.

$$-7x+6125-3675=0$$

Add 6125 to -3675.

$$-7x+2450=0$$

Subtract 2450 from both sides of the equation.

$$-7x=-2450$$

Divide both sides by -7.

$$x=350$$

The system is now solved.

$$x=350;y=\frac{6125}{4}$$