Solve {l}{4x-3y=11x}{10x+2y=-1x}

$$\left. \begin{array} { l } { 4 x - 3 y = 11 x } \\ { 10 x + 2 y = - 1 x } \end{array} \right.$$

Solve for x, y

$$x=0$$

$$y=0$$

Steps Using Substitution

Consider the first equation. Subtract 11x from both sides.

$$4x-3y-11x=0$$

Combine 4x and -11x to get -7x.

$$-7x-3y=0$$

Consider the second equation. Add x to both sides.

$$10x+2y+x=0$$

Combine 10x and x to get 11x.

$$11x+2y=0$$

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.

$$-7x-3y=0,11x+2y=0$$

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

$$-7x-3y=0$$

Add 3y to both sides of the equation.

$$-7x=3y$$

Divide both sides by -7.

$$x=-\frac{1}{7}\times 3y$$

Multiply -\frac{1}{7} times 3y.

$$x=-\frac{3}{7}y$$

Substitute -\frac{3y}{7} for x in the other equation, 11x+2y=0.

$$11\left(-\frac{3}{7}\right)y+2y=0$$

Multiply 11 times -\frac{3y}{7}.

$$-\frac{33}{7}y+2y=0$$

Add -\frac{33y}{7} to 2y.

$$-\frac{19}{7}y=0$$

Divide both sides of the equation by -\frac{19}{7}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=0$$

Substitute 0 for y in x=-\frac{3}{7}y. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=0$$

The system is now solved.

$$x=0,y=0$$

Steps Using Matrices

Consider the first equation. Subtract 11x from both sides.

$$4x-3y-11x=0$$

Combine 4x and -11x to get -7x.

$$-7x-3y=0$$

Consider the second equation. Add x to both sides.

$$10x+2y+x=0$$

Combine 10x and x to get 11x.

$$11x+2y=0$$

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

$$-7x-3y=0,11x+2y=0$$

Write the equations in matrix form.

$$\left(\begin{matrix}-7&-3\\11&2\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}0\\0\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}-7&-3\\11&2\end{matrix}\right).

$$inverse(\left(\begin{matrix}-7&-3\\11&2\end{matrix}\right))\left(\begin{matrix}-7&-3\\11&2\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}-7&-3\\11&2\end{matrix}\right))\left(\begin{matrix}0\\0\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}-7&-3\\11&2\end{matrix}\right))\left(\begin{matrix}0\\0\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}-7&-3\\11&2\end{matrix}\right))\left(\begin{matrix}0\\0\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{2}{-7\times 2-\left(-3\times 11\right)}&-\frac{-3}{-7\times 2-\left(-3\times 11\right)}\\-\frac{11}{-7\times 2-\left(-3\times 11\right)}&-\frac{7}{-7\times 2-\left(-3\times 11\right)}\end{matrix}\right)\left(\begin{matrix}0\\0\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{2}{19}&\frac{3}{19}\\-\frac{11}{19}&-\frac{7}{19}\end{matrix}\right)\left(\begin{matrix}0\\0\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}0\\0\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=0,y=0$$

Steps Using Elimination

Consider the first equation. Subtract 11x from both sides.

$$4x-3y-11x=0$$

Combine 4x and -11x to get -7x.

$$-7x-3y=0$$

Consider the second equation. Add x to both sides.

$$10x+2y+x=0$$

Combine 10x and x to get 11x.

$$11x+2y=0$$

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.

$$-7x-3y=0,11x+2y=0$$

To make -7x and 11x equal, multiply all terms on each side of the first equation by 11 and all terms on each side of the second by -7.

$$11\left(-7\right)x+11\left(-3\right)y=0,-7\times 11x-7\times 2y=0$$

Simplify.

$$-77x-33y=0,-77x-14y=0$$

Subtract -77x-14y=0 from -77x-33y=0 by subtracting like terms on each side of the equal sign.

$$-77x+77x-33y+14y=0$$

Add -77x to 77x. Terms -77x and 77x cancel out, leaving an equation with only one variable that can be solved.

$$-33y+14y=0$$

Add -33y to 14y.

$$-19y=0$$

Divide both sides by -19.

$$y=0$$

Substitute 0 for y in 11x+2y=0. Because the resulting equation contains only one variable, you can solve for x directly.

$$11x=0$$

Divide both sides by 11.

$$x=0$$

The system is now solved.

$$x=0,y=0$$