Chapter 4: Problem 63
Solve by graphing. $$ \begin{aligned} 5 x+2 y &=20 \\ -3 x-4 y &=-12 \end{aligned} $$
Short Answer
Expert verified
The solution is where the lines intersect: (4, -2).
Step by step solution
01
– Rewrite Equations in Slope-Intercept Form
To graph the equations, first express them in the slope-intercept form, which is \(y = mx + b\). Start with the first equation: \[5x + 2y = 20\]Solving for y:\[2y = -5x + 20\]\[y = -\frac{5}{2}x + 10\]Next, take the second equation: \[-3x - 4y = -12\]Solving for y:\[-4y = 3x - 12\]\[y = -\frac{3}{4}x + 3\]
02
– Plot the Y-Intercepts
For the first equation \(y = -\frac{5}{2}x + 10\), plot the y-intercept (0, 10). For the second equation \(y = -\frac{3}{4}x + 3\), plot the y-intercept (0, 3).
03
– Use the Slopes to Plot Another Point
For the first equation, the slope is \(-\frac{5}{2}\). This means for each 2 units moved to the right, move 5 units down. Plot another point using this slope. For the second equation, the slope is \(-\frac{3}{4}\). This means for each 4 units moved to the right, move 3 units down. Plot another point using this slope.
04
– Draw the Lines
Draw straight lines through the points plotted for each equation. Extend the lines until they intersect.
05
– Identify the Intersection Point
The solution to the system of equations is the point where the lines intersect. Locate this point on the graph.
06
– Verify the Solution
Verify that the coordinates of the intersection satisfy both original equations.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
slope-intercept form
The slope-intercept form of a linear equation is a way to express the equation of a line. The general form is: \( y = mx + b \) Here, \( m \) represents the slope of the line, and \( b \) represents the y-intercept. Converting to slope-intercept form helps us easily identify the slope and y-intercept for graphing.
For example, starting with the equations from the problem:
For example, starting with the equations from the problem:
- First equation: \(5x + 2y = 20\)
- Second equation: \(-3x - 4y = -12\)
- \(2y = -5x + 20\)
- \(y = -\frac{5}{2} x + 10\)
- \(-4y = 3x - 12\)
- \(y = -\frac{3}{4} x + 3\)
plotting y-intercepts
Once the equations are in slope-intercept form, we can easily find the y-intercepts. The y-intercept is the value of \( y \) when \( x = 0 \). In the slope-intercept form \( y = mx + b \), the y-intercept is simply \( b \). From the slope-intercept forms:
- First equation: \( y = -\frac{5}{2} x + 10 \)
- Second equation: \( y = -\frac{3}{4} x + 3 \)
- (0, 10) for the first equation.
- (0, 3) for the second equation.
graphing linear equations
To graph linear equations, we use the slope and y-intercept. Once the y-intercept is plotted, we use the slope to determine another point.
For each slope:
Let's add these points to our graph:
For each slope:
- \( y = -\frac{5}{2} x + 10 \): Slope is \(-\frac{5}{2}\). This means for every 2 units we move right on the x-axis, we move 5 units down on the y-axis.
- \( y = -\frac{3}{4} x + 3 \): Slope is \(-\frac{3}{4}\). This means for every 4 units we move right on the x-axis, we move 3 units down on the y-axis.
Let's add these points to our graph:
- For \( y = -\frac{5}{2} x + 10 \): Start at (0,10), next point is (2, 5).
- For \( y = -\frac{3}{4} x + 3 \): Start at (0,3), next point is (4, 0).
intersection of lines
The intersection of two lines on a graph represents the solution to a system of linear equations. It is the point where both equations meet, meaning it satisfies both equations simultaneously.
After graphing the lines:
Verify the solution by plugging these coordinates into both original equations to ensure they hold true:
After graphing the lines:
- The first line \( y = -\frac{5}{2} x + 10 \) passes through points (0, 10) and (2, 5).
- The second line \( y = -\frac{3}{4} x + 3 \) passes through points (0, 3) and (4, 0).
Verify the solution by plugging these coordinates into both original equations to ensure they hold true:
- \(5(4) + 2(-2) = 20\)
- \(-3(4) - 4(-2) = -12\)