Chapter 4: Problem 488
Find the equation of each line. Write the equation in slope-intercept form. \(m=-\frac{3}{4}\), containing point (8,-5)
Short Answer
Expert verified
The equation is \( y = -\frac{3}{4}x + 1 \).
Step by step solution
01
- Recall Slope-Intercept Form
The slope-intercept form of a linear equation is given by the formula \[ y = mx + b \]where \( m \) is the slope and \( b \) is the y-intercept.
02
- Substitute Slope and Point into the Equation
Substitute the slope \( m = -\frac{3}{4} \) and the point (8, -5) into the equation to find \( b \). Use the equation \( y = mx + b \). Therefore,\[ -5 = -\frac{3}{4}(8) + b \]
03
- Solve for y-Intercept \( b \)
Now, solve for \( b \). Start by multiplying:\[ -5 = -6 + b \]Add 6 to both sides:\[ b = 1 \]
04
- Write the Final Equation
Now that we have the slope \( m \) and the y-intercept \( b \), we can write the equation in slope-intercept form:\[ y = -\frac{3}{4}x + 1 \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
linear equation
A linear equation is an equation that models a straight line on a graph. The simplest and most common format for a linear equation is the slope-intercept form, represented as \[ y = mx + b \].
- Here, \( y \) is the dependent variable or the output.
- \( x \) is the independent variable or the input.
- \( m \) stands for the slope of the line.
- \( b \) is the y-intercept, which is the point where the line crosses the y-axis.
finding slope
The slope (\( m \)) of a linear equation measures how steep the line is. It is calculated as the ratio of the change in the y-values to the change in the x-values between two points on the line. Mathematically, it is expressed as \[ m = \frac{\Delta y}{\Delta x} = \frac{y_2 - y_1}{x_2 - x_1} \].
- A positive slope indicates an upward trend from left to right.
- A negative slope indicates a downward trend from left to right.
- A slope of zero indicates a horizontal line.
- An undefined slope indicates a vertical line.
solving for y-intercept
The y-intercept (\( b \)) is the point where the line crosses the y-axis (\( x = 0 \)). To find the y-intercept in a given problem, you can use the slope-intercept form equation: \[ y = mx + b \].
Substitute the given slope and the coordinates of a point (\( x, y \)) on the line into the equation. For example, in the exercise, we substitute \( m = -\frac{3}{4} \) and the point (8, -5) into the equation so we can solve for \( b \):
\[ -5 = -\frac{3}{4} (8) + b \]
Solve the resultant equation step-by-step:
So, we have:
\[ -5 = -6 + b\]
\[ -5 + 6 = b \]
\[ b = 1 \]
Therefore, the y-intercept \( b \) is 1.
Substitute the given slope and the coordinates of a point (\( x, y \)) on the line into the equation. For example, in the exercise, we substitute \( m = -\frac{3}{4} \) and the point (8, -5) into the equation so we can solve for \( b \):
\[ -5 = -\frac{3}{4} (8) + b \]
Solve the resultant equation step-by-step:
- First, calculate \( -\frac{3}{4} (8) \) which results in -6.
- Next, add 6 to both sides to isolate \( b \).
So, we have:
\[ -5 = -6 + b\]
\[ -5 + 6 = b \]
\[ b = 1 \]
Therefore, the y-intercept \( b \) is 1.
point-slope form
The point-slope form is another way to write the equation of a line, especially useful when you know the slope and one point on the line. The formula is given by:
\[ y - y_1 = m(x - x_1) \]
where:
\[ y + 5 = -\frac{3}{4}(x - 8) \]
This equation is useful and can be converted back to slope-intercept form (\( y = mx + b \)) by distributing and then solving for y.
\[ y - y_1 = m(x - x_1) \]
where:
- \( y_1 \) is the y-coordinate of the known point.
- \( m \) is the slope.
- \( x_1 \) is the x-coordinate of the known point.
\[ y + 5 = -\frac{3}{4}(x - 8) \]
This equation is useful and can be converted back to slope-intercept form (\( y = mx + b \)) by distributing and then solving for y.