Chapter 1: Problem 64
Find a linear equation whose graph is the straight line with the given properties. Through \((1,-4)\) and \((-1,-1)\)
Short Answer
Expert verified
The equation of the straight line that passes through the given points \((1, -4)\) and \((-1, -1)\) is \(y = -\frac{3}{2}x -\frac{5}{2}\).
Step by step solution
01
Find the slope (m) between the given points
To find the slope of the line passing through the given points \((1, -4)\) and \((-1, -1)\), we can use the formula:
\(m = \frac{y_2 - y_1}{x_2 - x_1}\)
Here, \((x_1, y_1) = (1, -4)\) and \((x_2, y_2) = (-1, -1)\). Now, substitute the values and solve for the value of \(m\):
\(m = \frac{-1 - (-4)}{-1 - 1} = \frac{3}{-2} = -\frac{3}{2}\)
The slope of the line is \(-\frac{3}{2}\).
02
Find the y-intercept (b) using slope-intercept form
Now it's time to find the y-intercept of the line. We can use either of the given points for this step. Let's use the point \((1, -4)\). The slope-intercept form of the line is given by:
\(y = mx + b\)
Replace \(x\), \(y\), and \(m\) with the values we have found so far:
\(-4 = -\frac{3}{2}(1) + b\)
Now solve for \(b\):
\(b = -4 + \frac{3}{2} = -\frac{5}{2}\)
The y-intercept of the line is \(-\frac{5}{2}\).
03
Write the equation of the line
Finally, we have the slope and y-intercept of the line. Plug these values into the slope-intercept equation \(y = mx + b\):
\(y = -\frac{3}{2}x -\frac{5}{2}\)
So, the equation of the straight line that passes through the given points \((1, -4)\) and \((-1, -1)\) is:
\(y = -\frac{3}{2}x -\frac{5}{2}\)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Slope of a Line
Understanding the slope of a line is foundational in algebra and helps us to grasp how steep a line is when graphed. The slope is represented by the letter m and is calculated as the rise over the run between two points on the line. In other words, it's the change in the y-coordinate (vertical change) divided by the change in the x-coordinate (horizontal change).
The formula to find the slope m between two points \( (x_1, y_1) \) and \( (x_2, y_2) \) is:
\[ m = \frac{y_2 - y_1}{x_2 - x_1} \]
For example, with the points \( (1, -4) \) and \( (-1, -1) \), we get a slope of \( -\frac{3}{2} \). This negative sign shows that the line is inclining downwards as it moves from left to right.
The formula to find the slope m between two points \( (x_1, y_1) \) and \( (x_2, y_2) \) is:
\[ m = \frac{y_2 - y_1}{x_2 - x_1} \]
For example, with the points \( (1, -4) \) and \( (-1, -1) \), we get a slope of \( -\frac{3}{2} \). This negative sign shows that the line is inclining downwards as it moves from left to right.
Y-intercept
Every linear equation graph crosses the y-axis at a certain point called the y-intercept, denoted as \( b \). It indicates the value of \( y \) when \( x = 0 \). To find the y-intercept using a point \((x, y)\) on the line and the slope \(m\), we substitute these values into the slope-intercept form \(y = mx + b\) and solve for \(b\).
In our example, substituting \( -4 \) for \(y\), \( -\frac{3}{2} \) for \(m\), and \(1\) for \(x\), we can solve for \(b\):
\[ b = -4 + \frac{3}{2} \]
This calculation reveals that the y-intercept is \(-\frac{5}{2}\). This is the point where the line will cross the y-axis, which is crucial for graphing the linear equation.
In our example, substituting \( -4 \) for \(y\), \( -\frac{3}{2} \) for \(m\), and \(1\) for \(x\), we can solve for \(b\):
\[ b = -4 + \frac{3}{2} \]
This calculation reveals that the y-intercept is \(-\frac{5}{2}\). This is the point where the line will cross the y-axis, which is crucial for graphing the linear equation.
Slope-Intercept Form
The slope-intercept form is a way of writing a linear equation that makes it particularly easy to graph. This form is \(y = mx + b\), where \(m\) is the slope and \(b\) is the y-intercept. It clearly shows the steepness of the line and where it intersects the y-axis.
Manipulating this formula allows us to isolate \(y\) and reveal the direction and initial value of the line. For instance, in our exercise, the final linear equation becomes: \[ y = -\frac{3}{2}x -\frac{5}{2} \]. The negative slope indicates a downward direction, and the y-intercept tells us that the line starts at the point \((0, -\frac{5}{2})\) on the y-axis.
Manipulating this formula allows us to isolate \(y\) and reveal the direction and initial value of the line. For instance, in our exercise, the final linear equation becomes: \[ y = -\frac{3}{2}x -\frac{5}{2} \]. The negative slope indicates a downward direction, and the y-intercept tells us that the line starts at the point \((0, -\frac{5}{2})\) on the y-axis.
Graphing Linear Equations
When it comes to graphing linear equations, knowing the slope and y-intercept is immensely helpful. To plot the line, follow these steps: Start by plotting the y-intercept on the vertical axis. Using our example, you would place a point at \((0, -\frac{5}{2})\). Then, use the slope to determine the rise over run from that point. With a slope of \( -\frac{3}{2} \), we'd move down 3 units and to the right 2 units to plot a second point.
Once you have at least two points marked on the graph, simply connect them with a straight line, extending it in both directions. Always remember that a linear equation will produce a straight line, and every point on that line is a solution to the equation.
Once you have at least two points marked on the graph, simply connect them with a straight line, extending it in both directions. Always remember that a linear equation will produce a straight line, and every point on that line is a solution to the equation.