Chapter 5: Problem 10
For the following exercises, find the inverse of the function on the given domain. $$ f(x)=9-x^{2},[0, \infty) $$
Short Answer
Expert verified
The inverse function is \( f^{-1}(y) = \sqrt{9 - y} \) with domain \( [0, 9] \).
Step by step solution
01
Understand the Function
The function given is \( f(x) = 9 - x^2 \) with the domain \([0, \infty)\). This means \( x \) can take any non-negative real number. This ensures that the function is not multi-valued over this domain, as it's a part of a downward-opening parabola restricted to its non-negative half.
02
Set Up the Equation for Inversion
To find the inverse, swap \( f(x) \) and \( x \). In other words, let \( y = 9 - x^2 \). For inversion, solve for \( x \) in terms of \( y \): \( x = 9 - y \).
03
Solve for x in Terms of y
Rearrange the equation \( y = 9 - x^2 \) to solve it for \( x \). We have: \( x^2 = 9 - y \). Thus, \( x = \sqrt{9 - y} \). Since the domain of \( x \) is non-negative, take the positive root.
04
Define the Inverse Function
The inverse function is where you solved for \( x \) in terms of \( y \). Therefore, the inverse function is \( f^{-1}(y) = \sqrt{9 - y} \). Note that the range of \( f^{-1}(y) \) is \([0, 3]\) because \( y \) in the function \( f(x) = 9 - x^2 \) varies from 9 to 0 as \( x \) goes from 0 to 3.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Domain and Range
In the realm of functions, the terms **domain** and **range** have specific meanings that help us understand what values the function can accept and produce. Let's say we're working with a function like \[ f(x) = 9 - x^2 \]
- Domain: This refers to all the possible values that can be plugged into the function for the variable, usually referred to as \( x \). For the above function, the domain is given as \([0, \infty)\). This means \( x \) can take all non-negative real numbers. The domain is crucial because it ensures the function is not ambiguous, or multi-valued, even though squared terms generally produce parabola shapes that can be symmetrical.
- Range: These are the possible values that the function can output, known as \( f(x) \). For \[ f(x) = 9 - x^2 \] with the specified domain, the range becomes \([0, 9]\). As \( x \) increases from 0 to a higher value, \( f(x) \) decreases from 9 to 0, defining its specific range.
Function Inversion
Function inversion is taking a function and flipping it over its domain and range, producing its 'opposite' or inverse function. If we start with a function like \[ f(x) = 9 - x^2 \] function inversion involves switching the input \( x \) with the output \( f(x) = y \).Here's how we find the inverse:
- Step 1: Replace \( f(x) \) with \( y \), giving us \[ y = 9 - x^2 \].
- Step 2: Solve for \( x \) in terms of \( y \): Rearrange the equation to \[ x^2 = 9 - y \], then solve for \( x \) to get \[ x = \sqrt{9 - y} \].
- Step 3: The positive square root is taken because the domain \([0, \infty)\) ensures \( x \) values are non-negative.
- Step 4: The inverse function is then \[ f^{-1}(y) = \sqrt{9 - y} \].
Quadratic Functions
Quadratic functions are among the most fundamental types of polynomial functions. They have a standard form that looks like this: \[ f(x) = ax^2 + bx + c \].These functions graph as parabola shapes, which can either open upwards or downwards, depending on the sign of the \( a \) coefficient.For the quadratic function \[ f(x) = 9 - x^2 \], we observe the following:
- Downward Opening: The negative sign before \( x^2 \) indicates that the parabola opens downward.
- Vertex Formed: This specific type, \[ f(x) = 9 - x^2 \], can also be rewritten as \[ x^2 - 9 \]. This reveals its vertex, located at (0,9), which is its maximum point due to the downward opening.
- Symmetry: Quadratics are symmetric around their vertex. In our case, the function's restriction to \([0, \infty)\) removes the left half of the symmetry, simplifying analysis and ensuring non-negative value handling.