Chapter 1: Problem 24
In each part, classify the lines as parallel, perpendicular, or neither. (a) \(y=-5 x+1\) and \(y=3-5 x\) (b) \(y-1=2(x-3)\) and \(y-4=-\frac{1}{2}(x+7)\) (c) \(4 x+5 y+7=0\) and \(5 x-4 y+9=0\) (d) \(A x+B y+C=0\) and \(A x+B y+D=0\) (e) \(y=\frac{1}{2} x\) and \(x=\frac{1}{2} y\)
Short Answer
Expert verified
(a) Parallel; (b) Perpendicular; (c) Perpendicular; (d) Parallel; (e) Neither.
Step by step solution
01
Identify Slope of Each Line
The slope-intercept form of a line is given by \( y = mx + b \), where \( m \) is the slope. For lines given in point-slope form or standard form, convert to slope-intercept form to find the slope. The slopes of parallel lines are equal, while the product of the slopes of perpendicular lines is -1.
02
Evaluate Part (a)
Both lines are in slope-intercept form: \( y = -5x + 1 \) and \( y = -5x + 3 \). The slope \( m \) of each line is \(-5\). Since the slopes are equal, the lines are parallel.
03
Evaluate Part (b)
Convert both equations to slope-intercept form. For \( y - 1 = 2(x - 3) \), simplify to get \( y = 2x - 5 \), with slope \( m = 2 \). For \( y - 4 = -\frac{1}{2}(x + 7) \), simplify to get \( y = -\frac{1}{2}x + \frac{7}{2} + 4 \) and further simplify to \( y = -\frac{1}{2}x + \frac{15}{2} \), with slope \( m = -\frac{1}{2} \). The product \( 2 \times -\frac{1}{2} = -1 \) indicates the lines are perpendicular.
04
Evaluate Part (c)
First, rewrite both equations in slope-intercept form. For \( 4x + 5y + 7 = 0 \), simplify to get \( y = -\frac{4}{5}x - \frac{7}{5} \), giving a slope of \(-\frac{4}{5} \). For \( 5x - 4y + 9 = 0 \), simplify to \( y = \frac{5}{4}x + \frac{9}{4} \), giving a slope of \( \frac{5}{4} \). The product \(-\frac{4}{5} \times \frac{5}{4} = -1 \), so the lines are perpendicular.
05
Evaluate Part (d)
Both equations are in the form \( Ax + By + C = 0 \) and \( Ax + By + D = 0 \). Since the coefficients of \( x \) and \( y \) are identical, the lines have the same slope and are parallel unless \( C = D \), whereby they are identical lines.
06
Evaluate Part (e)
The first line \( y = \frac{1}{2}x \) is already in slope-intercept form with a slope of \( \frac{1}{2} \). The second line \( x = \frac{1}{2}y \) can be rewritten as \( y = 2x \), giving a slope of \( 2 \). The product \( \frac{1}{2} \times 2 = 1 \) shows they are neither parallel nor perpendicular as the product is not -1.
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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 popular way to express the equation of a straight line. It is given as \(y = mx + b\), where:
- \(m\) represents the slope of the line.
- \(b\) is the y-intercept, the point where the line crosses the y-axis.
Standard Form
The standard form of a linear equation is \(Ax + By = C\). This format can sometimes make solving certain types of problems easier, particularly those involving systems of equations. Here, \(A\), \(B\), and \(C\) are integers, and \(A\) should typically be positive.
- Lines in standard form can be turned into slope-intercept form by solving for \(y\). For example, \(4x + 5y = 20\) could be rearranged to \(y = -\frac{4}{5}x + 4\).
- The form allows easy determination of both x- and y-intercepts by setting either variable to zero.
Point-Slope Form
Point-slope form is another way to express the equation of a straight line and is particularly helpful when you know one point on the line and the slope. The formula is written as \(y - y_1 = m(x - x_1)\), where:
- \(m\) is the slope of the line.
- \((x_1, y_1)\) is a known point on the line.
Slope Calculation
The slope of a line measures its steepness and direction. It can be calculated when two points on the line are known using the formula \(m = \frac{y_2 - y_1}{x_2 - x_1}\). The slope \(m\) is:
- Positive if the line ascends from left to right.
- Negative if the line descends from left to right.
- Zero if the line is horizontal, indicating no change in y-values as x-values increase.
- Undefined for vertical lines, since division by zero occurs \((x_2 - x_1 = 0)\).
Linear Equations
Linear equations form the basis for straight lines on a graph and can be expressed in multiple forms including slope-intercept, standard, and point-slope. The presence of a linear equation indicates a constant rate of change, signifying that the graph's inclination remains consistent throughout.
- They simplify the determination of relationships between variables.
- Graphically, each solution of the equation corresponds to a point on the line.