Systems of Equations contains two or more equations with the same variables. Learn how to solve systems of equations.

## Step by step guide to solve systems of equations

- A system of equations contains two equations with similar two variables. For example, consider the system of equations: \(x -y=1, x+y=5\)
- The easiest way to solve a system of equation is using the elimination method. The elimination method uses the addition property of equality. You can add the same value to each side of an equation.
- For the first equation above, you can add \(x+y\) to the left side and \(5\) to the right side of the first equation: \(x-y+(x+y)=1+5\). Now, if you simplify, you get: \(x-y+(x+y)=1+5→2x=6→x=3\). Now, substitute \(3\) for the \(x \) in the first equation: \(3-y=1\) . By solving this equation, \(y=2\)

### Example 1:

What is the value of \(x+y\) in this system of equations? \(\begin{cases}2x+5y=11 \\ 4x-2y=-26\end{cases}\)

**Solution:**

Solving Systems of Equations by Elimination

Multiply the first equation by \((−2)\), then add it to the second equation.

\(\cfrac{\begin{align} -2(2x+5y=11) \\ 4x-2y=- \ 26 \end{align}}{}\Rightarrow \cfrac{\begin{align} -4x-10y=- \ 22 \\ 4x-2y=- \ 26 \end{align}}{}\Rightarrow -12y=-48\Rightarrow y=4\)

Plug in the value of \(y\) into one of the equations and solve for \(x\).

\(2x+5(4)= 11 ⇒ 2x+20= 11 ⇒ 2x=-9 ⇒ x=- \ 4.5\)

Thus, \(x+y=-4.5+4=- \ 0.5\)

### Example 2:

What is the value of \(x\) and \(y\) in this system of equations? \(\begin{cases}3x-4y= \ -20 \\ -x+2y=10\end{cases}\)

**Solution:**

Solving Systems of Equations by Elimination: \(\begin{cases}3x-4y= \ -20 \\ -x+2y=10\end{cases} \Rightarrow\) Multiply the first equation by \(3\), then add it to the second equation.

\(\begin{cases}3x-4y= \ -20 \\ 3(-x+2y=10)\end{cases} \Rightarrow \begin{cases}3x-4y= \ -20 \\ -3x+6y=30\end{cases} \Rightarrow 2y=10 \Rightarrow y=5\)

Now, substitute \(5\) for \(y\) in the first equation and solve for \(x. 3x−4(5)= −20→3x−20=−20→x=0\)

## Exercises

### Solve each system of equations.

- \(\color{blue}{-4x-6y=7 \ \ \ \ \ x= \\ x-2y=7 \ \ \ \ \ y=} \\\ \)
- \(\color{blue}{-5x+y=-3 \ \ \ \ \ x= \\ 3x-7y=21 \ \ \ \ \ y= } \\\ \)
- \(\color{blue}{3y= -6x+12 \ \ \ \ \ x= \\ 8x-9y=-10 \ \ \ \ \ y= } \\\ \)
- \(\color{blue}{x+15y=50 \ \ \ \ \ x= \\ x+10y=40 \ \ \ \ \ y= } \\\ \)
- \(\color{blue}{3x-2y=15 \ \ \ \ \ x= \\ 3x-5y=15 \ \ \ \ \ y= } \\\ \)
- \(\color{blue}{3x-6y=-12 \ \ \ \ \ x= \\ -x-3y=-6 \ \ \ \ \ y= } \\\ \)

### Download Systems of Equations Worksheet

## Answers

- \(\color{blue}{x=2,y=-\frac{5}{2}}\)
- \(\color{blue}{x=0,y=-3}\)
- \(\color{blue}{x=1,y=2}\)
- \(\color{blue}{x=20,y=2}\)
- \(\color{blue}{x=5,y=0}\)
- \(\color{blue}{x=0,y=2}\)