Chapter 8: Problem 38
Solve each system by addition. Determine whether each system is independent, dependent, or inconsistent. $$\begin{aligned} &3 x-2 y=7\\\ &-3 x+y=5 \end{aligned}$$
Short Answer
Expert verified
x = -\frac{17}{3}, y = -12; independent
Step by step solution
01
- Align the Equations
Write the given system of equations in a clear format:\[\begin{aligned}3x - 2y &= 7 \-3x + y &= 5\end{aligned}\]
02
- Add the Equations
To eliminate one of the variables, add the two equations together:\[\begin{aligned}3x - 2y + (-3x + y) &= 7 + 5 \3x - 3x - 2y + y &= 12 \- y &= 12\end{aligned}\]
03
- Solve for y
Simplify the equation to solve for \(y\):\[-y = 12 \ y = -12\]
04
- Substitute y into One of the Original Equations
Choose the second equation to substitute \( y = -12 \):\[-3x + y = 5 \-3x - 12 = 5 \-3x = 17 \x = -\frac{17}{3}\]
05
- Verify the Solution
Substitute \( x = -\frac{17}{3} \) and \( y = -12 \) back into the original equations to verify:For the first equation:\[3\left(-\frac{17}{3}\right) - 2(-12) = 7 \-17 + 24 = 7 \7 = 7 \ \text{Correct}\]For the second equation:\[-3\left(-\frac{17}{3}\right) + (-12) = 5 \17 - 12 = 5 \5 = 5 \ \text{Correct}\]
06
- Classify the System
Since the solution \(x = -\frac{17}{3}\) and \( y = -12 \) satisfies both equations, the system is independent.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding the Addition Method
The addition method, also known as the elimination method, is a powerful technique for solving systems of linear equations. It involves combining the equations in such a way that one of the variables is eliminated.
Here's a step-by-step breakdown:
\(\begin{aligned} 3x - 2y &= 7 \ -3x + y &= 5 \text{Adding these gives}\ -y &= 12 \ y &= -12 \ \text{We then solve for } x: \ \ -3x + (-12) = 5 \ x = - \frac {17}{3}\) This method is highly efficient and easy to learn with practice.
Here's a step-by-step breakdown:
- Align the equations: Write both equations so that their corresponding terms line up vertically.
- Add the equations: Combine like terms from both equations. This helps to eliminate one variable.
- Solve for the remaining variable: Simplify the resulting equation to find the value of one variable.
- Substitute back: Insert the found value into one of the original equations to solve for the other variable.
\(\begin{aligned} 3x - 2y &= 7 \ -3x + y &= 5 \text{Adding these gives}\ -y &= 12 \ y &= -12 \ \text{We then solve for } x: \ \ -3x + (-12) = 5 \ x = - \frac {17}{3}\) This method is highly efficient and easy to learn with practice.
Dependent vs. Independent Systems
Understanding whether a system of equations is independent, dependent, or inconsistent is crucial in algebra.
- Independent Systems: An independent system has exactly one unique solution. This means the lines representing the equations intersect at exactly one point. In our example, the system is independent because we found a unique solution: \(x = -\frac{17}{3}\) and \(y = -12\).
- Dependent Systems: A dependent system has infinitely many solutions. This occurs when the equations represent the same line, meaning every point on the line is a solution. In such cases, after attempting to eliminate a variable, you'd end up with a true but redundant statement like \(0 = 0\).
- Inconsistent Systems: An inconsistent system has no solution because the lines are parallel and never intersect. This will result in a false statement like \(0 = 5\) when attempting to solve the system.
Verifying Solutions to Systems of Equations
Verifying solutions ensures the values found actually satisfy the original equations. Here’s how you can double-check your work:
- Substitute the values: Take the solution pair \((x, y)\) and substitute the values back into both original equations.
- Simplify both equations: Perform the indicated operations to see if both equations result in true statements.