Chapter 1: Problem 30
Find the inverse function of \(f\). Graph (by hand) \(f\) and \(f^{-1}\). Describe the relationship between the graphs. $$ f(x)=x^{3}-1 $$
Short Answer
Expert verified
The inverse function of \(f(x) = x^3 - 1\) is \(f^{-1}(x) = (x + 1)^{1/3}\). The graph of the inverse function is the reflection of the original function over the line \(y=x\).
Step by step solution
01
Define the function
The given function is \(f(x) = x^3 - 1\). We start by rewriting this as \(y = x^3 - 1\)
02
Swap x and y to find inverse
To find the inverse of a function, the roles of \(x\) and \(y\) are swapped. Thus, the equation becomes \(x = y^3 - 1\).
03
Solve for y
Next, solve for \(y\) by adding 1 to both sides of the equation and taking the cube root of both sides. The equation becomes \(y = (x + 1)^{1/3}\). This is the inverse function, denoted as \(f^{-1}(x) = (x + 1)^{1/3}\).
04
Graph both functions
To graph the functions, choose a suitable range for \(x\) and draw both functions. The function \(f(x) = x^3 - 1\) is a cubic function shifted 1 unit down, while \(f^{-1}(x) = (x+1)^{1/3}\) is a cube root function shifted 1 unit to the left.
05
Describe the relationship between the graphs
If the graphs were plotted on the same graph, it would be observed that the graph of \(f^{-1}(x)\) is a reflection of the graph of \(f(x)\) over the line \(y=x\). In more practical terms, for any point on the graph of \(f\), a point with inverted coordinates is on the graph of \(f^{-1}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Function Graphing
Graphing a function involves plotting its values on a coordinate plane. In the case of a function like \(f(x) = x^3 - 1\), we will need to select appropriate \(x\)-values and use them to compute \(y\)-values by substituting into the function. Each pair \((x, f(x))\) defines a point on the graph.
When graphing an inverse function,\(f^{-1}(x)\), follow a similar method, using the right equation to get the corresponding \(y\)-values. For \(f^{-1}(x) = (x + 1)^{1/3}\), you will plot points \((x, (x + 1)^{1/3})\). It's helpful to find several points for both \(f(x)\) and \(f^{-1}(x)\) to accurately reflect the shapes of the graphs.
When graphing an inverse function,\(f^{-1}(x)\), follow a similar method, using the right equation to get the corresponding \(y\)-values. For \(f^{-1}(x) = (x + 1)^{1/3}\), you will plot points \((x, (x + 1)^{1/3})\). It's helpful to find several points for both \(f(x)\) and \(f^{-1}(x)\) to accurately reflect the shapes of the graphs.
- Label each axis clearly, typically with \(x\) on the horizontal axis and \(y\) on the vertical axis.
- Mark key points like intercepts and any points where the behavior of the function notably changes.
- Draw smooth curves through the points, remembering to consider the general shape and behavior of the function type, such as whether it increases, decreases, approaches asymptotes, etc.
Cubic Function
A cubic function is a type of polynomial of degree three, typically of the form \(f(x) = ax^3 + bx^2 + cx + d\). In this exercise, the function \(f(x) = x^3 - 1\) features a cubic term with a coefficient of 1, and a constant term of -1.
Total behavior of cubic functions is interesting. They usually feature:
Total behavior of cubic functions is interesting. They usually feature:
- An S-shaped curve that can change direction once.
- They can have up to three real roots, although our function \(x^3 - 1\) is shifted such that it has a root at \(x = 1\).
- A point of inflection where the curve changes concavity.
Cube Root Function
A cube root function, like \(f^{-1}(x) = (x+1)^{1/3}\), involves taking the cube root of the expression within the function. This operation is the inverse of cubing a number, which is how the function \(f(x) = x^3 - 1\) is inverted to obtain \(f^{-1}(x)\).
Cube root functions have distinctive characteristics:
Cube root functions have distinctive characteristics:
- Their graphs also have an S-shape, similar to cubic functions, but the curve is horizontal rather than vertical.
- The domain and range of cube root functions are all real numbers since you can take the cube root of any real number.
- They also have a point of inflection where they change concavity, making them symmetrical.
Reflection Over Line y = x
When two functions are inverses of each other, their graphs exhibit a special mirror-like symmetry over the line \(y = x\). Each point \((a, b)\) on one graph corresponds to \((b, a)\) on the other graph. This is because their roles (x and y values) are switched in inverse functions.
Visualizing this, if you fold the plane along the line \(y = x\), both graphs will overlap exactly. You can observe this reflection in the given exercise, where the graph of \(f(x) = x^3 - 1\) reflects perfectly over \(y = x\) into the graph of \(f^{-1}(x) = (x+1)^{1/3}\).
Visualizing this, if you fold the plane along the line \(y = x\), both graphs will overlap exactly. You can observe this reflection in the given exercise, where the graph of \(f(x) = x^3 - 1\) reflects perfectly over \(y = x\) into the graph of \(f^{-1}(x) = (x+1)^{1/3}\).
- This concept is critical as it helps confirm that you've calculated the inverse correctly.
- Seeing this relationship visually reinforces understanding of the algebraic manipulation involved in finding inverses.