Question

By sketching a graph of \(y=3 x-1\) show that this is a one-to-one function.

Short answer

Explain your reasoning based on the graph of the function. Answer: Yes, the function \(y = 3x - 1\) is a one-to-one function because it is a linear function with a non-zero slope. This means that each x-element in the domain is paired with a unique y-element in the codomain, ensuring there are no horizontal segments on the graph, and no two points have the same y-value.

Step-by-step solution

Understanding the function

The given function is \(y = 3x - 1\), which represents a linear function with a slope of 3 and a y-intercept at -1.

Determine the points to plot on the graph

It's helpful to choose a few points from the domain of the function to plot on the graph. For example, we can choose -1, 0, 1, and 2 as x-values, and then find the corresponding y-values using the function. For \(x = -1\), we have \(y = 3(-1) - 1 = -3 - 1 = -4\) For \(x = 0\), we have \(y = 3(0) - 1 = -1\) For \(x = 1\), we have \(y = 3(1) - 1 = 3 - 1 = 2\) For \(x = 2\), we have \(y = 3(2) - 1 = 6 - 1 = 5\)

Plot the points on the graph

Plot the points we found above on a graph: \((-1, -4)\), \((0, -1)\), \((1, 2)\), and \((2, 5)\).

Draw the line through the plotted points

Connect the plotted points with a straight line, as this is a linear function. This line should have an upward slope due to the positive coefficient (3) of the x-term.

Analyze the graph for one-to-one function

Observe the graph and check if any two points have the same y-value. Since the function is linear and has a non-zero slope, it will not have any horizontal segments, which means each x-element is paired with a unique y-element. Thus, the function is a one-to-one function.

Key concepts

Linear Function

A linear function is one of the simplest forms of functions in algebra. It’s an equation that forms a straight line when graphed. The general form of a linear function is \(y = mx + b\), where \(m\) is the slope and \(b\) is the y-intercept.

- **Characteristics**: Because it creates a line, every change in \(x\) results in a consistent change in \(y\). This predictability is what characterizes linear functions.
- **Examples**: If you encounter any equation that can be rewritten to conform to the \(y = mx + b\) format, you have a linear function. For instance, \(y = 3x - 1\) is already in this form and thus is a linear function.

Linear functions are fundamental in understanding more complex mathematical concepts because they introduce basic graphing concepts, such as slopes and intercepts. When faced with a new problem, recognizing when you have a linear function can simplify the steps needed to solve it. Remember, if your graph forms a straight line without any curves, you are dealing with a linear function!

Graph Sketching

Graph sketching involves plotting the function on a coordinate plane to visualize its behavior. For the function \(y = 3x - 1\), the process requires selecting points, calculating their corresponding \(y\)-values, and then drawing a line through these points.

- **Steps for Graph Sketching**:

• Choose a set of \(x\)-values. For simplicity, select integers like -1, 0, 1, and 2. They are easy to calculate and help define the graph sufficiently.
• Calculate the corresponding \(y\)-values using the function. For example, if \(x = 0\), then \(y = 3(0) - 1 = -1\).
• Plot these points on a graph. In the example, popular points are \((-1, -4), (0, -1), (1, 2), (2, 5)\).
• Connect the points with a straight line. This connection should reflect a straight line without any breaks or curves, as this is a defining feature of linear functions.

Graph sketching is not just about drawing. It helps us interpret the function and see relationships between variables. Whether it’s to confirm a function's behavior or to check if it's one-to-one, sketching offers clarity.

Slope and Intercept

Within the equation of a linear function \(y = mx + b\), two critical components are the slope \(m\) and the y-intercept \(b\). They define the line's shape and position on the graph.

- **Slope \(m\)**: This value determines the line's steepness and direction. A positive slope means the line rises as it moves from left to right; a negative slope indicates a downward trend. For \(y = 3x - 1\), the slope is 3, signaling a steep upward climb.
- **Y-intercept \(b\)**: This is the point where the line crosses the y-axis. For our function, \(b = -1\), meaning the line intersects the axis at \( (0, -1)\).

Understanding slope and intercept is essential as they quickly convey much information about the line. Knowing the slope and intercept allows you to visualize the graph even before sketching, making solving linear equations more intuitive. These elements also play a significant role in identifying whether a function is one-to-one, helping determine its injectivity and whether it passes the vertical line test without overlapping.