Problem 14 - College Algebra with Corequisite Support

Question

For the following exercises, find the inverse of the functions. $$ f(x)=4-x^{3} $$

Step-by-Step Solution

Answer

The inverse of the function is \( f^{-1}(x) = (4-x)^{1/3} \).

Step 1: Define Function as y

Start by setting the function equal to y: \[ y = 4 - x^3 \] This makes it easier to manipulate the equation to solve for x.

Step 2: Solve for x

Rearrange the equation to express x in terms of y:1. Subtract 4 from both sides: \[ y - 4 = -x^3 \]2. Multiply by -1 to get positive \( x^3 \): \[ 4 - y = x^3 \]3. Take the cube root of both sides: \[ x = (4 - y)^{1/3} \] Now x is expressed in terms of y.

Step 3: Write the Inverse Function

Swap the variables to express the inverse function:Since \( x = (4 - y)^{1/3} \), the inverse function is:\[ f^{-1}(y) = (4 - y)^{1/3} \] Replace y with x to get the final form:\[ f^{-1}(x) = (4 - x)^{1/3} \]

Key Concepts

Algebraic Manipulation

Algebraic manipulation is the heart of solving mathematical equations and expressions. It involves performing operations on both sides of an equation to isolate a variable or simplify the expression. In the case of finding the inverse function, algebraic manipulation helps us express one variable in terms of another.To start, you'll often set the function equal to a variable, like y, making it easier to switch perspective and solve for x. Then, to express x in terms of y, you use techniques such as:

• Adding or subtracting a number from both sides to move terms around.
• Dividing or multiplying both sides by a number to simplify the equation.
• Taking roots or powers to solve for the variable of interest.

In our exercise, we see these manipulations take shape by rearranging the function from \(y = 4 - x^3\) to \(x = (4 - y)^{1/3}\), paving the way to define the inverse function neatly.

Function Notation

Function notation is a key concept in algebra and calculus. It provides a clear and concise way to denote and work with functions. When we write a function as \(f(x)\), it signifies that f is a function depending on the variable x. This notation becomes particularly handy when dealing with inverse functions. To find an inverse, we swap our original function's inputs and outputs. For instance, the function \(f(x) = 4 - x^3\) is swapped to become \(f^{-1}(x) = (4 - x)^{1/3}\). The notation \(f^{-1}(x)\) is crucial because it shows the transformation clearly:

• The original function maps x to \(4 - x^3\).
• The inverse maps \(4 - x^3\) back to x, reversing the effect of the original function.

This harmony and transition between functions illustrate how swapping the roles of x and y helps redefine the relationships between inputs and outputs in function notation.

Cube Roots

Cube roots appear when you need to "undo" the operation of cubing a number. In simple terms, the cube root of a number \(a\) is a number \(b\) such that \(b^3 = a\). In mathematics, cube roots are shown using the notation \(a^{1/3}\). Thankfully, unlike square roots which can be positive or negative, every real number has a single real cube root.In the context of inverse functions, cube roots become essential when reversing equations involving cubic powers. In our problem, once we rearranged our function to \(4 - y = x^3\), taking the cube root of both sides was a necessary step:

• Cube the root of both sides to solve for x in terms of y.
• Recognizing the cube root allows us to express the inverse function cleanly and concisely.

Taking cube roots ensures we've effectively "unwrapped" the cubic transformation imposed by the original function, leading us to the inverse function \(f^{-1}(x) = (4 - x)^{1/3}\).