Chapter 3: Problem 32
Find an equation of the line passing through each pair of points. Write the equation in the form \(A x+B y=C .\) See Example 5. $$ (6,2) \text { and }(8,8) $$
Short Answer
Expert verified
The equation is \(3x - y = 16\).
Step by step solution
01
Determine the Slope
To find the equation of the line passing through two points, first compute the slope, \(m\), using the formula: \[ m = \frac{y_2 - y_1}{x_2 - x_1} \] where \((x_1, y_1) = (6, 2)\) and \((x_2, y_2) = (8, 8)\). Substituting in these values gives: \[ m = \frac{8 - 2}{8 - 6} = \frac{6}{2} = 3 \]. Thus, the slope \(m\) is 3.
02
Use Point-Slope Form
Use the point-slope formula to write the equation of the line: \[ y - y_1 = m(x - x_1) \]. Using \(m = 3\) and \((x_1, y_1) = (6, 2)\), the equation becomes \[ y - 2 = 3(x - 6) \].
03
Simplify to Slope-Intercept Form
Distribute and simplify the equation to move into slope-intercept form \(y = mx + b\): \[ y - 2 = 3x - 18 \]. Adding 2 to both sides gives \[ y = 3x - 16 \].
04
Convert to Standard Form
The standard form of a line's equation is \(Ax + By = C\). Rearrange \(y = 3x - 16\) into this form by moving all terms to one side: \[-3x + y = -16 \]. To avoid negative coefficients where possible, multiply the entire equation by -1: \[ 3x - y = 16 \].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Slope
When learning about the equation of a line, the concept of slope is foundational. The slope, often denoted as \( m \), measures the steepness of a line. It tells us how much \( y \) changes for a given change in \( x \). The formula to calculate the slope between two points \((x_1, y_1)\) and \((x_2, y_2)\) is: \[ m = \frac{y_2 - y_1}{x_2 - x_1} \] This formula essentially gives the vertical change (rise) divided by the horizontal change (run).
- A positive slope means the line rises as it moves from left to right.
- A negative slope means the line falls as it moves from left to right.
- If the slope is zero, the line is horizontal.
- If the line is vertical, the slope is undefined.
Point-Slope Form
The point-slope form is incredibly useful for writing the equation of a line when you have a point and a slope. The form of the point-slope equation is: \[ y - y_1 = m(x - x_1) \] This equation uses:
- \((x_1, y_1)\) - a known point on the line.
- \( m \) - the slope of the line.
Slope-Intercept Form
The slope-intercept form is perhaps the most popular way to express the equation of a line for its simplicity and clarity. The form is: \[ y = mx + b \] Here, \( m \) is the slope, and \( b \) is the y-intercept — the point where the line crosses the y-axis. This form is perfect for quickly graphing a line. Just start at the y-intercept (\( b \)) and use the slope \( m \) to find other points. By converting \( y - 2 = 3(x - 6) \) into slope-intercept form, we distribute and simplify to find:
- Original: \( y - 2 = 3x - 18 \)
- Add 2 to both sides: \( y = 3x - 16 \)
Standard Form
The standard form of a line's equation provides a neat, general way to express lines, especially helpful for linear equations in different mathematical contexts. The standard form is given by: \[ Ax + By = C \] Here, \( A \), \( B \), and \( C \) are integers, and the coefficients are typically adjusted to keep \( A \) non-negative. Converting from slope-intercept form \( y = 3x - 16 \) to standard form involves rearranging the terms:
- Original: \( y = 3x - 16 \)
- Rearrange: \(-3x + y = -16 \)
- To avoid negative coefficients, multiply by \(-1\): \( 3x - y = 16 \)