Solve {l}{m+x-m=2(x-2m)}{2(3x+4m)=3m+2(x-1)}

$$\left\{ \begin{array} { l } { m + x - m = 2 ( x - 2 m ) } \\ { 2 ( 3 x + 4 m ) = 3 m + 2 ( x - 1 ) } \end{array} \right.$$

Solve for m, x

$$x=-\frac{8}{21}\approx -0.380952381$$

$$m=-\frac{2}{21}\approx -0.095238095$$

Steps Using Substitution

Consider the first equation. Combine m and -m to get 0.

$$x=2\left(x-2m\right)$$

Use the distributive property to multiply 2 by x-2m.

$$x=2x-4m$$

Subtract 2x from both sides.

$$x-2x=-4m$$

Combine x and -2x to get -x.

$$-x=-4m$$

Divide both sides by -1.

$$x=-\left(-4\right)m$$

Multiply -1 times -4m.

$$x=4m$$

Substitute 4m for x in the other equation, 4x+5m=-2.

$$4\times 4m+5m=-2$$

Multiply 4 times 4m.

$$16m+5m=-2$$

Add 16m to 5m.

$$21m=-2$$

Divide both sides by 21.

$$m=-\frac{2}{21}$$

Substitute -\frac{2}{21} for m in x=4m. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=4\left(-\frac{2}{21}\right)$$

Multiply 4 times -\frac{2}{21}.

$$x=-\frac{8}{21}$$

The system is now solved.

$$x=-\frac{8}{21},m=-\frac{2}{21}$$

Steps Using Matrices

Consider the first equation. Combine m and -m to get 0.

$$x=2\left(x-2m\right)$$

Use the distributive property to multiply 2 by x-2m.

$$x=2x-4m$$

Subtract 2x from both sides.

$$x-2x=-4m$$

Combine x and -2x to get -x.

$$-x=-4m$$

Add 4m to both sides.

$$-x+4m=0$$

Consider the second equation. Use the distributive property to multiply 2 by 3x+4m.

$$6x+8m=3m+2\left(x-1\right)$$

Use the distributive property to multiply 2 by x-1.

$$6x+8m=3m+2x-2$$

Subtract 3m from both sides.

$$6x+8m-3m=2x-2$$

Combine 8m and -3m to get 5m.

$$6x+5m=2x-2$$

Subtract 2x from both sides.

$$6x+5m-2x=-2$$

Combine 6x and -2x to get 4x.

$$4x+5m=-2$$

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

$$-x+4m=0,4x+5m=-2$$

Write the equations in matrix form.

$$\left(\begin{matrix}-1&4\\4&5\end{matrix}\right)\left(\begin{matrix}x\\m\end{matrix}\right)=\left(\begin{matrix}0\\-2\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}-1&4\\4&5\end{matrix}\right).

$$inverse(\left(\begin{matrix}-1&4\\4&5\end{matrix}\right))\left(\begin{matrix}-1&4\\4&5\end{matrix}\right)\left(\begin{matrix}x\\m\end{matrix}\right)=inverse(\left(\begin{matrix}-1&4\\4&5\end{matrix}\right))\left(\begin{matrix}0\\-2\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\m\end{matrix}\right)=inverse(\left(\begin{matrix}-1&4\\4&5\end{matrix}\right))\left(\begin{matrix}0\\-2\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\m\end{matrix}\right)=inverse(\left(\begin{matrix}-1&4\\4&5\end{matrix}\right))\left(\begin{matrix}0\\-2\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\m\end{matrix}\right)=\left(\begin{matrix}\frac{5}{-5-4\times 4}&-\frac{4}{-5-4\times 4}\\-\frac{4}{-5-4\times 4}&-\frac{1}{-5-4\times 4}\end{matrix}\right)\left(\begin{matrix}0\\-2\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\m\end{matrix}\right)=\left(\begin{matrix}-\frac{5}{21}&\frac{4}{21}\\\frac{4}{21}&\frac{1}{21}\end{matrix}\right)\left(\begin{matrix}0\\-2\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\m\end{matrix}\right)=\left(\begin{matrix}\frac{4}{21}\left(-2\right)\\\frac{1}{21}\left(-2\right)\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\m\end{matrix}\right)=\left(\begin{matrix}-\frac{8}{21}\\-\frac{2}{21}\end{matrix}\right)$$

Extract the matrix elements x and m.

$$x=-\frac{8}{21},m=-\frac{2}{21}$$

Steps Using Elimination

Consider the first equation. Combine m and -m to get 0.

$$x=2\left(x-2m\right)$$

Use the distributive property to multiply 2 by x-2m.

$$x=2x-4m$$

Subtract 2x from both sides.

$$x-2x=-4m$$

Combine x and -2x to get -x.

$$-x=-4m$$

Add 4m to both sides.

$$-x+4m=0$$

Consider the second equation. Use the distributive property to multiply 2 by 3x+4m.

$$6x+8m=3m+2\left(x-1\right)$$

Use the distributive property to multiply 2 by x-1.

$$6x+8m=3m+2x-2$$

Subtract 3m from both sides.

$$6x+8m-3m=2x-2$$

Combine 8m and -3m to get 5m.

$$6x+5m=2x-2$$

Subtract 2x from both sides.

$$6x+5m-2x=-2$$

Combine 6x and -2x to get 4x.

$$4x+5m=-2$$

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.

$$-x+4m=0,4x+5m=-2$$

To make -x and 4x equal, multiply all terms on each side of the first equation by 4 and all terms on each side of the second by -1.

$$4\left(-1\right)x+4\times 4m=0,-4x-5m=-\left(-2\right)$$

Simplify.

$$-4x+16m=0,-4x-5m=2$$

Subtract -4x-5m=2 from -4x+16m=0 by subtracting like terms on each side of the equal sign.

$$-4x+4x+16m+5m=-2$$

Add -4x to 4x. Terms -4x and 4x cancel out, leaving an equation with only one variable that can be solved.

$$16m+5m=-2$$

Add 16m to 5m.

$$21m=-2$$

Divide both sides by 21.

$$m=-\frac{2}{21}$$

Substitute -\frac{2}{21} for m in 4x+5m=-2. Because the resulting equation contains only one variable, you can solve for x directly.

$$4x+5\left(-\frac{2}{21}\right)=-2$$

Multiply 5 times -\frac{2}{21}.

$$4x-\frac{10}{21}=-2$$

Add \frac{10}{21} to both sides of the equation.

$$4x=-\frac{32}{21}$$

Divide both sides by 4.

$$x=-\frac{8}{21}$$

The system is now solved.

$$x=-\frac{8}{21},m=-\frac{2}{21}$$