\left\{ \begin{array} { l } { 3 x + 2 y = 152 } \\ { 2 x + 4 y = 192 } \end{array} \right.
Solve for x, y
x=28
y=34
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3x+2y=152,2x+4y=192
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.
3x+2y=152
Choose one of the equations and solve it for x by isolating x on the left hand side of the equal sign.
3x=-2y+152
Subtract 2y from both sides of the equation.
x=\frac{1}{3}\left(-2y+152\right)
Divide both sides by 3.
x=-\frac{2}{3}y+\frac{152}{3}
Multiply \frac{1}{3} times -2y+152.
2\left(-\frac{2}{3}y+\frac{152}{3}\right)+4y=192
Substitute \frac{-2y+152}{3} for x in the other equation, 2x+4y=192.
-\frac{4}{3}y+\frac{304}{3}+4y=192
Multiply 2 times \frac{-2y+152}{3}.
\frac{8}{3}y+\frac{304}{3}=192
Add -\frac{4y}{3} to 4y.
\frac{8}{3}y=\frac{272}{3}
Subtract \frac{304}{3} from both sides of the equation.
y=34
Divide both sides of the equation by \frac{8}{3}, which is the same as multiplying both sides by the reciprocal of the fraction.
x=-\frac{2}{3}\times 34+\frac{152}{3}
Substitute 34 for y in x=-\frac{2}{3}y+\frac{152}{3}. Because the resulting equation contains only one variable, you can solve for x directly.
x=\frac{-68+152}{3}
Multiply -\frac{2}{3} times 34.
x=28
Add \frac{152}{3} to -\frac{68}{3} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.
x=28,y=34
The system is now solved.
3x+2y=152,2x+4y=192
Put the equations in standard form and then use matrices to solve the system of equations.
\left(\begin{matrix}3&2\\2&4\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}152\\192\end{matrix}\right)
Write the equations in matrix form.
inverse(\left(\begin{matrix}3&2\\2&4\end{matrix}\right))\left(\begin{matrix}3&2\\2&4\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}3&2\\2&4\end{matrix}\right))\left(\begin{matrix}152\\192\end{matrix}\right)
Left multiply the equation by the inverse matrix of \left(\begin{matrix}3&2\\2&4\end{matrix}\right).
\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}3&2\\2&4\end{matrix}\right))\left(\begin{matrix}152\\192\end{matrix}\right)
The product of a matrix and its inverse is the identity matrix.
\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}3&2\\2&4\end{matrix}\right))\left(\begin{matrix}152\\192\end{matrix}\right)
Multiply the matrices on the left hand side of the equal sign.
\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{4}{3\times 4-2\times 2}&-\frac{2}{3\times 4-2\times 2}\\-\frac{2}{3\times 4-2\times 2}&\frac{3}{3\times 4-2\times 2}\end{matrix}\right)\left(\begin{matrix}152\\192\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{1}{2}&-\frac{1}{4}\\-\frac{1}{4}&\frac{3}{8}\end{matrix}\right)\left(\begin{matrix}152\\192\end{matrix}\right)
Do the arithmetic.
\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{1}{2}\times 152-\frac{1}{4}\times 192\\-\frac{1}{4}\times 152+\frac{3}{8}\times 192\end{matrix}\right)
Multiply the matrices.
\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}28\\34\end{matrix}\right)
Do the arithmetic.
x=28,y=34
Extract the matrix elements x and y.
3x+2y=152,2x+4y=192
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.
2\times 3x+2\times 2y=2\times 152,3\times 2x+3\times 4y=3\times 192
To make 3x and 2x equal, multiply all terms on each side of the first equation by 2 and all terms on each side of the second by 3.
6x+4y=304,6x+12y=576
Simplify.
6x-6x+4y-12y=304-576
Subtract 6x+12y=576 from 6x+4y=304 by subtracting like terms on each side of the equal sign.
4y-12y=304-576
Add 6x to -6x. Terms 6x and -6x cancel out, leaving an equation with only one variable that can be solved.
-8y=304-576
Add 4y to -12y.
-8y=-272
Add 304 to -576.
y=34
Divide both sides by -8.
2x+4\times 34=192
Substitute 34 for y in 2x+4y=192. Because the resulting equation contains only one variable, you can solve for x directly.
2x+136=192
Multiply 4 times 34.
2x=56
Subtract 136 from both sides of the equation.
x=28
Divide both sides by 2.
x=28,y=34
The system is now solved.
Examples
Quadratic equation
{ x } ^ { 2 } - 4 x - 5 = 0
Trigonometry
4 \sin \theta \cos \theta = 2 \sin \theta
Linear equation
y = 3x + 4
Arithmetic
699 * 533
Matrix
\left[ \begin{array} { l l } { 2 } & { 3 } \\ { 5 } & { 4 } \end{array} \right] \left[ \begin{array} { l l l } { 2 } & { 0 } & { 3 } \\ { -1 } & { 1 } & { 5 } \end{array} \right]
Simultaneous equation
\left. \begin{cases} { 8x+2y = 46 } \\ { 7x+3y = 47 } \end{cases} \right.
Differentiation
\frac { d } { d x } \frac { ( 3 x ^ { 2 } - 2 ) } { ( x - 5 ) }
Integration
\int _ { 0 } ^ { 1 } x e ^ { - x ^ { 2 } } d x
Limits
\lim _{x \rightarrow-3} \frac{x^{2}-9}{x^{2}+2 x-3}