Solve {l}{4x-3/9-2y-x/3=1-y/6}{4(y-1)-3(x+y)=-7-2y}

$$\left\{ \begin{array} { l } { \frac { 4 x - 3 } { 9 } - \frac { 2 y - x } { 3 } = 1 - \frac { y } { 6 } } \\ { 4 ( y - 1 ) - 3 ( x + y ) = - 7 - 2 y } \end{array} \right.$$

Solve for x, y

$$x=3$$

$$y=2$$

Steps Using Substitution

Consider the first equation. Multiply both sides of the equation by 18, the least common multiple of 9,3,6.

$$2\left(4x-3\right)-6\left(2y-x\right)=18-3y$$

Use the distributive property to multiply 2 by 4x-3.

$$8x-6-6\left(2y-x\right)=18-3y$$

Use the distributive property to multiply -6 by 2y-x.

$$8x-6-12y+6x=18-3y$$

Combine 8x and 6x to get 14x.

$$14x-6-12y=18-3y$$

Add 3y to both sides.

$$14x-6-12y+3y=18$$

Combine -12y and 3y to get -9y.

$$14x-6-9y=18$$

Add 6 to both sides.

$$14x-9y=18+6$$

Add 18 and 6 to get 24.

$$14x-9y=24$$

Consider the second equation. Use the distributive property to multiply 4 by y-1.

$$4y-4-3\left(x+y\right)=-7-2y$$

Use the distributive property to multiply -3 by x+y.

$$4y-4-3x-3y=-7-2y$$

Combine 4y and -3y to get y.

$$y-4-3x=-7-2y$$

Add 2y to both sides.

$$y-4-3x+2y=-7$$

Combine y and 2y to get 3y.

$$3y-4-3x=-7$$

Add 4 to both sides.

$$3y-3x=-7+4$$

Add -7 and 4 to get -3.

$$3y-3x=-3$$

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.

$$14x-9y=24,-3x+3y=-3$$

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

$$14x-9y=24$$

Add 9y to both sides of the equation.

$$14x=9y+24$$

Divide both sides by 14.

$$x=\frac{1}{14}\left(9y+24\right)$$

Multiply \frac{1}{14} times 9y+24.

$$x=\frac{9}{14}y+\frac{12}{7}$$

Substitute \frac{9y}{14}+\frac{12}{7} for x in the other equation, -3x+3y=-3.

$$-3\left(\frac{9}{14}y+\frac{12}{7}\right)+3y=-3$$

Multiply -3 times \frac{9y}{14}+\frac{12}{7}.

$$-\frac{27}{14}y-\frac{36}{7}+3y=-3$$

Add -\frac{27y}{14} to 3y.

$$\frac{15}{14}y-\frac{36}{7}=-3$$

Add \frac{36}{7} to both sides of the equation.

$$\frac{15}{14}y=\frac{15}{7}$$

Divide both sides of the equation by \frac{15}{14}, which is the same as multiplying both sides by the reciprocal of the fraction.

$$y=2$$

Substitute 2 for y in x=\frac{9}{14}y+\frac{12}{7}. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=\frac{9}{14}\times 2+\frac{12}{7}$$

Multiply \frac{9}{14} times 2.

$$x=\frac{9+12}{7}$$

Add \frac{12}{7} to \frac{9}{7} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x=3$$

The system is now solved.

$$x=3,y=2$$

Steps Using Matrices

Consider the first equation. Multiply both sides of the equation by 18, the least common multiple of 9,3,6.

$$2\left(4x-3\right)-6\left(2y-x\right)=18-3y$$

Use the distributive property to multiply 2 by 4x-3.

$$8x-6-6\left(2y-x\right)=18-3y$$

Use the distributive property to multiply -6 by 2y-x.

$$8x-6-12y+6x=18-3y$$

Combine 8x and 6x to get 14x.

$$14x-6-12y=18-3y$$

Add 3y to both sides.

$$14x-6-12y+3y=18$$

Combine -12y and 3y to get -9y.

$$14x-6-9y=18$$

Add 6 to both sides.

$$14x-9y=18+6$$

Add 18 and 6 to get 24.

$$14x-9y=24$$

Consider the second equation. Use the distributive property to multiply 4 by y-1.

$$4y-4-3\left(x+y\right)=-7-2y$$

Use the distributive property to multiply -3 by x+y.

$$4y-4-3x-3y=-7-2y$$

Combine 4y and -3y to get y.

$$y-4-3x=-7-2y$$

Add 2y to both sides.

$$y-4-3x+2y=-7$$

Combine y and 2y to get 3y.

$$3y-4-3x=-7$$

Add 4 to both sides.

$$3y-3x=-7+4$$

Add -7 and 4 to get -3.

$$3y-3x=-3$$

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

$$14x-9y=24,-3x+3y=-3$$

Write the equations in matrix form.

$$\left(\begin{matrix}14&-9\\-3&3\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}24\\-3\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}14&-9\\-3&3\end{matrix}\right).

$$inverse(\left(\begin{matrix}14&-9\\-3&3\end{matrix}\right))\left(\begin{matrix}14&-9\\-3&3\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}14&-9\\-3&3\end{matrix}\right))\left(\begin{matrix}24\\-3\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}14&-9\\-3&3\end{matrix}\right))\left(\begin{matrix}24\\-3\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}14&-9\\-3&3\end{matrix}\right))\left(\begin{matrix}24\\-3\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{3}{14\times 3-\left(-9\left(-3\right)\right)}&-\frac{-9}{14\times 3-\left(-9\left(-3\right)\right)}\\-\frac{-3}{14\times 3-\left(-9\left(-3\right)\right)}&\frac{14}{14\times 3-\left(-9\left(-3\right)\right)}\end{matrix}\right)\left(\begin{matrix}24\\-3\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{1}{5}&\frac{3}{5}\\\frac{1}{5}&\frac{14}{15}\end{matrix}\right)\left(\begin{matrix}24\\-3\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{1}{5}\times 24+\frac{3}{5}\left(-3\right)\\\frac{1}{5}\times 24+\frac{14}{15}\left(-3\right)\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}3\\2\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=3,y=2$$

Steps Using Elimination

Consider the first equation. Multiply both sides of the equation by 18, the least common multiple of 9,3,6.

$$2\left(4x-3\right)-6\left(2y-x\right)=18-3y$$

Use the distributive property to multiply 2 by 4x-3.

$$8x-6-6\left(2y-x\right)=18-3y$$

Use the distributive property to multiply -6 by 2y-x.

$$8x-6-12y+6x=18-3y$$

Combine 8x and 6x to get 14x.

$$14x-6-12y=18-3y$$

Add 3y to both sides.

$$14x-6-12y+3y=18$$

Combine -12y and 3y to get -9y.

$$14x-6-9y=18$$

Add 6 to both sides.

$$14x-9y=18+6$$

Add 18 and 6 to get 24.

$$14x-9y=24$$

Consider the second equation. Use the distributive property to multiply 4 by y-1.

$$4y-4-3\left(x+y\right)=-7-2y$$

Use the distributive property to multiply -3 by x+y.

$$4y-4-3x-3y=-7-2y$$

Combine 4y and -3y to get y.

$$y-4-3x=-7-2y$$

Add 2y to both sides.

$$y-4-3x+2y=-7$$

Combine y and 2y to get 3y.

$$3y-4-3x=-7$$

Add 4 to both sides.

$$3y-3x=-7+4$$

Add -7 and 4 to get -3.

$$3y-3x=-3$$

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.

$$14x-9y=24,-3x+3y=-3$$

To make 14x and -3x equal, multiply all terms on each side of the first equation by -3 and all terms on each side of the second by 14.

$$-3\times 14x-3\left(-9\right)y=-3\times 24,14\left(-3\right)x+14\times 3y=14\left(-3\right)$$

Simplify.

$$-42x+27y=-72,-42x+42y=-42$$

Subtract -42x+42y=-42 from -42x+27y=-72 by subtracting like terms on each side of the equal sign.

$$-42x+42x+27y-42y=-72+42$$

Add -42x to 42x. Terms -42x and 42x cancel out, leaving an equation with only one variable that can be solved.

$$27y-42y=-72+42$$

Add 27y to -42y.

$$-15y=-72+42$$

Add -72 to 42.

$$-15y=-30$$

Divide both sides by -15.

$$y=2$$

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

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

Multiply 3 times 2.

$$-3x+6=-3$$

Subtract 6 from both sides of the equation.

$$-3x=-9$$

Divide both sides by -3.

$$x=3$$

The system is now solved.

$$x=3,y=2$$