Chapter 5.4, Problem 9E

To determine

ToSolve:The system of linear equations

  $y=-2x-4$

  $y=2x-4$

Answer to Problem 9E

The solution of the given system of linear equations is $\left(x,y\right)=\left(0,-4\right)$

Explanation of Solution

Given:

The system of linear equations

  $y=-2x-4$

  $y=2x-4$

Concept Used:

In solving a system of linear equation by substitution method. The value of one of the unknown from any of the equation is substituted into another equation and the value of second unknown is calculated.

The calculated value of second unknown is then substituted into any of the equation to find the value of the first unknown.

Calculation:

Given the system of linear equations

  $y=-2x-4\text{- - - - - }\left(1\right)$

  $y=2x-4\text{ - - - - - }\left(2\right)$

Using the Substitution method

Substituting the value of $y$ from equation $\left(1\right)$ into the equation $\left(2\right)$ , we have

  $\begin{array}{c}y=2x-4\\ -2x-4=2x-4\text{ Substitue }-2x-4\text{ for }y\\ -2x-4+4=2x-4+4\text{ Add }4\text{ to both sides}\\ -2x=2x\end{array}$

  $\begin{array}{c}-2x-2x=2x-2x\text{ Subtrct }2x\text{ from both sides}\\ -4x=0\\ \frac{-4x}{-4}=\frac{0}{-4}\text{ Divide both sides by }-4\\ x=0\end{array}$

Substituting $x=0$ into equation $\left(1\right)$

  $\begin{array}{c}y=-2x-4\\ y=-2\left(0\right)-4\\ y=0-4\\ y=-4\end{array}$

Therefore, the solution of the given system of linear equations is $\left(x,y\right)=\left(0,-4\right)$

Conclusion:

The solution of the given system of linear equations is $\left(x,y\right)=\left(0,-4\right)$