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Ch. 2 - Graphs and Functions
Lial - College Algebra 13th Edition
Lial13th EditionCollege AlgebraISBN: 9780136881063Not the one you use?Change textbook
Chapter 3, Problem 67

For each line described, write an equation in (a) slope-intercept form, if possible, and (b) standard form. through (-7, 4), perpendicular to y = 8

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Identify the given line's equation: \( y = 8 \). This is a horizontal line where the slope \( m = 0 \).
Since the new line is perpendicular to \( y = 8 \), its slope will be the negative reciprocal of 0. The negative reciprocal of 0 is undefined, which means the new line is vertical.
A vertical line passing through the point \((-7, 4)\) has the equation \( x = -7 \). This cannot be written in slope-intercept form \( y = mx + b \) because the slope is undefined.
For the standard form of a vertical line, rewrite \( x = -7 \) as \( x + 0y = -7 \). This fits the standard form \( Ax + By = C \) where \( A = 1 \), \( B = 0 \), and \( C = -7 \).
Summarize: (a) Slope-intercept form is not possible for this vertical line, and (b) the standard form is \( x = -7 \) or equivalently \( x + 0y = -7 \).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Slope-Intercept Form

The slope-intercept form of a line is y = mx + b, where m represents the slope and b is the y-intercept. This form makes it easy to identify the slope and where the line crosses the y-axis, which is essential for graphing and understanding linear relationships.
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Slope-Intercept Form

Perpendicular Lines and Their Slopes

Two lines are perpendicular if the product of their slopes is -1. For a horizontal line like y = 8 (slope 0), the perpendicular line must be vertical, which has an undefined slope. Recognizing this helps determine the correct slope for the new line.
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Parallel & Perpendicular Lines

Standard Form of a Line

The standard form of a line is Ax + By = C, where A, B, and C are integers, and A ≥ 0. This form is useful for solving systems of equations and provides a clear, consistent way to represent lines, especially vertical or horizontal ones.
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