Chapter 2: Problem 56
Determine whether the graphs of each pair of equations are parallel, perpendicular, or neither. $$ 2 x+3 y=9,3 x-2 y=5 $$
Short Answer
Expert verified
The graphs are perpendicular because their slopes are opposite reciprocals.
Step by step solution
01
Rewrite the first equation in slope-intercept form
The first equation is \(2x + 3y = 9\). To convert this to the slope-intercept form \(y = mx + b\), solve for \(y\). \[2x + 3y = 9\] Subtract \(2x\) from both sides: \[3y = -2x + 9\] Now, divide each term by 3 to solve for \(y\): \[y = -\frac{2}{3}x + 3\] In this equation, the slope \(m\) is \(-\frac{2}{3}\).
02
Rewrite the second equation in slope-intercept form
The second equation is \(3x - 2y = 5\). Solve for \(y\) to convert it to slope-intercept form. \[3x - 2y = 5\] Subtract \(3x\) from both sides: \[-2y = -3x + 5\] Now, divide each term by -2: \[y = \frac{3}{2}x - \frac{5}{2}\] In this equation, the slope \(m\) is \(\frac{3}{2}\).
03
Compare the slopes to determine the relationship between the lines
The slope of the first line is \(-\frac{2}{3}\), and the slope of the second line is \(\frac{3}{2}\). Two lines are parallel if their slopes are equal, and they are perpendicular if the product of their slopes is \(-1\).
04
Check for perpendicularity
Calculate the product of the slopes: \(m_1 \times m_2 = -\frac{2}{3} \times \frac{3}{2}\). The product is \(-1\), which means these slopes are opposite reciprocals. Thus, the graphs of these equations are perpendicular.
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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 denoted as \(y = mx + b\), where \(m\) represents the slope, and \(b\) represents the y-intercept. The slope \(m\) determines the steepness of the line, showing how much \(y\) changes with a change in \(x\). Meanwhile, the y-intercept \(b\) is the point where the line crosses the y-axis. Knowing how to convert a linear equation into this form is crucial. It allows you to quickly determine and graph the line based on its slope and y-intercept.
- First, isolate \(y\) on one side of the equation.
- Ensure that \(y\) is by itself, then express the remaining terms in the form \(mx+b\).
Parallel Lines
Parallel lines have the distinct characteristic of having the same slope \(m\). This means they never intersect, no matter how far they are extended on a graph. If you see two lines with equal slopes in their slope-intercept forms, you can be sure they are parallel.
- You'll often encounter parallel lines in problems involving systems of equations.
- Parallel lines demonstrate a consistent rate of change without intersecting.
Perpendicular Lines
Perpendicular lines intersect at a right angle (90 degrees). A key feature of perpendicular lines is the relationship between their slopes; they are opposite reciprocals. If you multiply the slopes of two perpendicular lines, the product is \(-1\).
- If the slope of one line is \(\frac{a}{b}\), the slope of another line that is perpendicular will be \(-\frac{b}{a}\).
- This opposite reciprocal relationship is a quick check for perpendicularity.
Graphing Linear Equations
Graphing linear equations involves plotting points that line up to form a straight line. Once in the slope-intercept form, \(y=mx+b\), plotting becomes simple:
- Start at the y-intercept \(b\) on the y-axis.
- From there, use the slope \(m\) to identify additional points. For a slope of \(\frac{3}{2}\), it means rising 3 units for every 2 units you move right.