Chapter 3: Problem 72
Find the slope and the y-intercept of the graph of each equation and graph it. See Examples 4 and 5. $$ 2 x+3 y=9 $$
Short Answer
Expert verified
The slope is \(-\frac{2}{3}\) and the y-intercept is 3.
Step by step solution
01
Convert to Slope-Intercept Form
First, we need to manipulate the given equation into the slope-intercept form, which is \( y = mx + b \), where \( m \) represents the slope and \( b \) the y-intercept. Start with the equation: \[ 2x + 3y = 9 \] Subtract \( 2x \) from both sides: \[ 3y = -2x + 9 \]Then, divide every term by 3 to solve for \( y \):\[ y = -\frac{2}{3}x + 3 \]
02
Identify the Slope and Y-intercept
From the equation \( y = -\frac{2}{3}x + 3 \), identify the slope \( m \) and the y-intercept \( b \):- The slope \( m \) is \(-\frac{2}{3}\).- The y-intercept \( b \) is 3.
03
Plot the Y-intercept
Start by plotting the y-intercept on the graph, which is the point where \( y = 3 \). This is the point \( (0, 3) \) on the y-axis.
04
Use the Slope to Plot Another Point
The slope \(-\frac{2}{3}\) means that for every 2 units you move down on the y-axis, you move 3 units to the right on the x-axis. From the y-intercept \( (0, 3) \), move down 2 units to \( y = 1 \) and 3 units to the right to \( x = 3 \). This gives you the point \( (3, 1) \) on the graph.
05
Draw the Line
Connect the two points \( (0, 3) \) and \( (3, 1) \) with a straight line. Extend the line in both directions, ensuring it passes through these two points. This line represents the graph of the equation \( 2x + 3y = 9 \).
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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 powerful and intuitive way to write equations of lines. This form is expressed as \( y = mx + b \). Here are the key components of this format:
- \( m \) represents the slope of the line, illustrating how steep the line is.
- \( b \) stands for the y-intercept, the point where the line crosses the y-axis.
Graphing Linear Equations
Graphing linear equations can be simplified by using the slope-intercept form, \( y = mx + b \). Once you have identified the slope and y-intercept from a given equation, you can plot it easily on a coordinate grid.
Here’s a simple guide to graphing:
Here’s a simple guide to graphing:
- Start by plotting the y-intercept \((0, b)\) on the y-axis. This tells you where to begin your line.
- Use the slope \( m \), often expressed as a fraction \( \frac{rise}{run} \), to determine the direction and steepness of the line. A negative slope, like \(-\frac{2}{3}\), indicates a line that falls as it moves from left to right.
- From the y-intercept, apply the slope. For a slope of \(-\frac{2}{3}\), move down 2 units and right 3 units to find your next point.
- After marking at least two points, draw a straight line through them to represent the entire equation.
Identifying Slope and Y-Intercept
In linear equations, identifying both the slope and y-intercept is a fundamental step in understanding and graphing these equations. These two values tell us a lot about the line:
- The slope\( (m) \) indicates the tilt or steepness of the line. A positive slope means the line rises from left to right, while a negative slope means it falls.
- The y-intercept\( (b) \) is where the line crosses the y-axis. It gives us a starting point to begin drawing our line on a graph.