Solve {l}{41x-19y=158}{49x-15y=158}

$$\left\{ \begin{array} { l } { 41 x - 19 y = 158 } \\ { 49 x - 15 y = 158 } \end{array} \right.$$

Solve for x, y

$$x=2$$

$$y=-4$$

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.

$$41x-19y=158,49x-15y=158$$

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

$$41x-19y=158$$

Add 19y to both sides of the equation.

$$41x=19y+158$$

Divide both sides by 41.

$$x=\frac{1}{41}\left(19y+158\right)$$

Multiply \frac{1}{41} times 19y+158.

$$x=\frac{19}{41}y+\frac{158}{41}$$

Substitute \frac{19y+158}{41} for x in the other equation, 49x-15y=158.

$$49\left(\frac{19}{41}y+\frac{158}{41}\right)-15y=158$$

Multiply 49 times \frac{19y+158}{41}.

$$\frac{931}{41}y+\frac{7742}{41}-15y=158$$

Add \frac{931y}{41} to -15y.

$$\frac{316}{41}y+\frac{7742}{41}=158$$

Subtract \frac{7742}{41} from both sides of the equation.

$$\frac{316}{41}y=-\frac{1264}{41}$$

Divide both sides of the equation by \frac{316}{41}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=-4$$

Substitute -4 for y in x=\frac{19}{41}y+\frac{158}{41}. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=\frac{19}{41}\left(-4\right)+\frac{158}{41}$$

Multiply \frac{19}{41} times -4.

$$x=\frac{-76+158}{41}$$

Add \frac{158}{41} to -\frac{76}{41} 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.

$$x=2,y=-4$$

Steps Using Matrices

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

$$41x-19y=158,49x-15y=158$$

Write the equations in matrix form.

$$\left(\begin{matrix}41&-19\\49&-15\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}158\\158\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}41&-19\\49&-15\end{matrix}\right).

$$inverse(\left(\begin{matrix}41&-19\\49&-15\end{matrix}\right))\left(\begin{matrix}41&-19\\49&-15\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}41&-19\\49&-15\end{matrix}\right))\left(\begin{matrix}158\\158\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}41&-19\\49&-15\end{matrix}\right))\left(\begin{matrix}158\\158\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}41&-19\\49&-15\end{matrix}\right))\left(\begin{matrix}158\\158\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}-\frac{15}{41\left(-15\right)-\left(-19\times 49\right)}&-\frac{-19}{41\left(-15\right)-\left(-19\times 49\right)}\\-\frac{49}{41\left(-15\right)-\left(-19\times 49\right)}&\frac{41}{41\left(-15\right)-\left(-19\times 49\right)}\end{matrix}\right)\left(\begin{matrix}158\\158\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}-\frac{15}{316}&\frac{19}{316}\\-\frac{49}{316}&\frac{41}{316}\end{matrix}\right)\left(\begin{matrix}158\\158\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}-\frac{15}{316}\times 158+\frac{19}{316}\times 158\\-\frac{49}{316}\times 158+\frac{41}{316}\times 158\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}2\\-4\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=2,y=-4$$

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.

$$41x-19y=158,49x-15y=158$$

To make 41x and 49x equal, multiply all terms on each side of the first equation by 49 and all terms on each side of the second by 41.

$$49\times 41x+49\left(-19\right)y=49\times 158,41\times 49x+41\left(-15\right)y=41\times 158$$

Simplify.

$$2009x-931y=7742,2009x-615y=6478$$

Subtract 2009x-615y=6478 from 2009x-931y=7742 by subtracting like terms on each side of the equal sign.

$$2009x-2009x-931y+615y=7742-6478$$

Add 2009x to -2009x. Terms 2009x and -2009x cancel out, leaving an equation with only one variable that can be solved.

$$-931y+615y=7742-6478$$

Add -931y to 615y.

$$-316y=7742-6478$$

Add 7742 to -6478.

$$-316y=1264$$

Divide both sides by -316.

$$y=-4$$

Substitute -4 for y in 49x-15y=158. Because the resulting equation contains only one variable, you can solve for x directly.

$$49x-15\left(-4\right)=158$$

Multiply -15 times -4.

$$49x+60=158$$

Subtract 60 from both sides of the equation.

$$49x=98$$

Divide both sides by 49.

$$x=2$$

The system is now solved.

$$x=2,y=-4$$