Finding and Verifying Inverse Functions

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Questions and Answers

If f(g(x)) and g(f(x)) both equal x, then the function g is the _____ function of the function f.

inverse

Find the inverse function of f informally. $f(x) = 3x + 1$

$f^{-1}(x) = \frac{x-1}{3}$

Find the inverse function of f informally. $f(x) = \frac{x-3}{9}$

$f^{-1}(x) = 9x+3$

Use the graph of the function to sketch the graph of its inverse function $y=f^{-1}(x)$.

<p>See image ① (F)</p> Signup and view all the answers

Use the table of values for y = f(x) to complete a table for y = f⁻¹(x).

<p>X: 5, 7, 9, 11, 13, 15; f⁻¹(x): -1, 0, 1, 2, 3, 4</p> Signup and view all the answers

Does the function have an inverse function?

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Use a graphing utility to graph the function. Use the Horizontal Line Test to determine whether the function has an inverse function. $g(x) = (x + 2)^2 + 3$

<p>The function is not one-to-one and so does not have an inverse function. (A)</p> Signup and view all the answers

Use a graphing utility to graph the function. Use the Horizontal Line Test to determine whether the function has an inverse function. $f(x) = (x + 3)^3$

<p>The function is one-to-one and so has an inverse function. (B)</p> Signup and view all the answers

Use a graphing utility to graph the function. Use the Horizontal Line Test to determine whether the function has an inverse function. $h(x) = x - \frac{6}{x+1} - 31$

<p>The function is one-to-one and so has an inverse function. (A)</p> Signup and view all the answers

Consider the following function. $f(x) = x^5 - 2$. Find the inverse function of f.

<p>$f^{-1}(x) = (x+2)^{1/5}$</p> Signup and view all the answers

Consider the following function. $f(x) = x^5 - 2$. Graph both f and f⁻¹ on the same set of coordinate axes.

<p>See image ① (B)</p> Signup and view all the answers

Consider the following function. $f(x) = x^5 - 2$. Describe the relationship between the graphs of f and f⁻¹.

<p>The graph of f⁻¹ is the reflection of f in the line y = x. (C)</p> Signup and view all the answers

Consider the following function. $f(x) = x^5 - 2$. State the domain and range of f. (Enter your answers using interval notation.)

<p>domain: (-∞, ∞); range: (-∞, ∞)</p> Signup and view all the answers

Consider the following function. $f(x) = x^{3/5}$. State the domain and range of f⁻¹. (Enter your answers using interval notation.)

<p>domain: (-∞, ∞); range: (-∞, ∞)</p> Signup and view all the answers

Determine whether the function has an inverse function. $f(x) = x^6$

<p>No, f does not have an inverse. (A)</p> Signup and view all the answers

If it does, then find the inverse function. (If an answer does not exist, enter DNE.) $f(x) = x^6$

<p>DNE</p> Signup and view all the answers

Determine whether the function has an inverse function. $g(x) = \frac{x + 1}{9}$

<p>Yes, g does have an inverse. (A)</p> Signup and view all the answers

If it does, then find the inverse function. (If an answer does not exist, enter DNE.) $g(x) = \frac{x + 1}{9}$

<p>$g^{-1}(x) = 9x-1$</p> Signup and view all the answers

Determine whether the function has an inverse function. $f(x) = \sqrt{x - 1}, x \ge 1$

<p>Yes, f does have an inverse. (A)</p> Signup and view all the answers

If it does, then find the inverse function. (If an answer does not exist, enter DNE.) $f(x) = \sqrt{x - 1}, x \ge 1$

<p>$f^{-1}(x) = x^2 + 1, x \ge 0$</p> Signup and view all the answers

Determine whether the function has an inverse function. $f(x) = \frac{4x + 7}{7x + 5}$

<p>Yes, f does have an inverse. (A)</p> Signup and view all the answers

If it does, then find the inverse function. (If an answer does not exist, enter DNE.) $f(x) = \frac{4x + 7}{7x + 5}$

<p>$f^{-1}(x) = \frac{7-5x}{7x-4}$</p> Signup and view all the answers

Determine whether the function has an inverse function. $f(x) = (x + 9)^2, x \ge -9$

<p>Yes, f does have an inverse. (B)</p> Signup and view all the answers

If it does, then find the inverse function. (If an answer does not exist, enter DNE.) $f(x) = (x + 9)^2, x \ge -9$

<p>$f^{-1}(x) = \sqrt{x} - 9, x \ge 0$</p> Signup and view all the answers

Use the functions f(x) = x + 5 and g(x) = 3x^6 to find each of the following functions. $f^{-1}(x) = $

<p>x-5</p> Signup and view all the answers

Use the functions f(x) = x + 5 and g(x) = 3x^6 to find each of the following functions. $(g^{-1} \omicron f^{-1})(x) = $

<p>$\sqrt[6]{\frac{x-5}{3}}$</p> Signup and view all the answers

The cost C for a business to make personalized T-shirts is given by $C(x) = 7.50x + 1500$ where x represents the number of T-shirts.

<p>The function $C$ = the graph m the function $C^{-1}$ = the graph n</p> Signup and view all the answers

Explain what C(x) and C⁻¹(x) represent in the context of the problem.

<p>C(x) represents the total cost of making x units of T-shirts. C⁻¹(x) represents the number of T-shirts that can be made for a given total cost. (E)</p> Signup and view all the answers

Flashcards

What is an inverse function?

If f(g(x)) and g(f(x)) both equal x, then the function g is the inverse function of the function f.

Informal Inverse Function

To find the inverse of a function informally, reverse the operations. For example, if f(x) = 3x + 1, then f⁻¹(x) = (x - 1)/3.

Horizontal Line Test purpose?

Use the horizontal line test on the graph of a function to determine if it has an inverse function. If any horizontal line intersects the graph more than once, the function does not have an inverse.

Graph of Inverse Functions

The graph of f⁻¹ is the reflection of f in the line y = x.

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Finding an Inverse Function

To find the inverse of f(x), switch x and y and solve for y.

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Table of Values for Inverse function

Given a table of values for y = f(x), create a table for y = f⁻¹(x) by swapping the inputs and outputs. x becomes f(x) and f(x) becomes x.

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Function is One-to-One

The function is one-to-one meaning it passes the horizontal line test, therefore it has an inverse function.

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Function is NOT One-to-One

The function is not one-to-one meaning it does not pass the horizontal line test, therefore it does not have an inverse function.

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Domain and Range

Domain includes all possible input values. Range contains all output values.

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Domain and Range of Inverse

The domain of f is the range of f-1, and the range of f is the domain of f-1.

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How to calculate Inverse functions

The inverse of f(x) = x + 5 is f⁻¹(x) = x - 5 and the inverse of g(x) = x^6 is g⁻¹(x) = x^(1/6).

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Study Notes

  • If f(g(x)) and g(f(x)) both equal x, then the function g is the inverse function of the function f.

Finding Inverse Functions Informally

  • To find the inverse function of f(x) = 3x + 1, first determine the the inverse function and then, verify that f(f⁻¹(x)) = x.
  • The inverse function of f(x) = 3x + 1 is f⁻¹(x) = (x-1)/3.
  • f(f⁻¹(x)) = 3((x-1)/3) + 1 = x - 1 + 1 = x.
  • To verify that f⁻¹(f(x)) = x, determine f⁻¹(f(x)) = ((3x + 1) - 1)/3 = 3x/3 = x.
  • The inverse function of f(x) = (x-3)/9 is f⁻¹(x) = 9x + 3.
  • f(f⁻¹(x)) = ((9x + 3) - 3) / 9 = 9x / 9 = x.
  • f⁻¹(f(x)) = 9((x-3)/9) + 3 = x - 3 + 3 = x.

Using Graphs to Sketch Inverse Functions

  • To sketch the graph of an inverse function y = f⁻¹(x), use the existing graph of the function.

Completing Tables for Inverse Functions

  • Given a table of values for y = f(x), a table for y = f⁻¹(x) can be completed by swapping the x and y values.
  • For instance, if f(x) has the points (-1, 5), (0, 7), (1, 9), (2, 11), (3, 13), and (4, 15), then f⁻¹(x) has the points (5, -1), (7, 0), (9, 1), (11, 2), (13, 3), and (15, 4).
  • Likewise if f(x) has the points (-4, 5), (-3, 0), (-2, -5), (-1, -10), (0, -15), and (1, -20), then f⁻¹(x) has the points (5, -4), (0, -3), (-5, -2), (-10, -1), (-15, 0), and (-20, 1).

Determining Existence of Inverse Functions

  • A function has an inverse function if it passes the horizontal line test.

Using Graphing Utilities and the Horizontal Line Test

  • Graphing utilities and the Horizontal Line Test can help determine if a function has an inverse function.
  • If a function is one-to-one (passes the horizontal line test), it has an inverse function.
  • If a function is not one-to-one (does not pass the horizontal line test), it does not have an inverse function.

Finding Inverse Functions Algebraically

  • The inverse function of f(x) = x⁵ - 2 is f⁻¹(x) = (x + 2)^(1/5).
  • The graph of f⁻¹ is the reflection of f in the line y = x. -The domain and range of both f and f⁻¹ are (-∞, ∞).
  • The inverse function of f(x) = x^(3/5) is f⁻¹(x) = x^(5/3).
  • The graph of f⁻¹ is the reflection of f in the line y = x.
  • The domain and range of both f and f⁻¹ are (-∞, ∞).

Determining if a Function has an Inverse

  • f(x) = x⁶ does not have an inverse.
  • g(x) = (x + 1)/9 has the inverse g⁻¹(x) = 9x - 1.
  • f(x) = 5x + 8 has the inverse f⁻¹(x) = (x - 8)/5.
  • f(x) = √(x - 1), x ≥ 1 , has the inverse f⁻¹(x) = x² + 1, x ≥ 0
  • f(x) = (4x + 7) / (7x + 5) has the inverse f⁻¹(x) = (7 - 5x) / (7x - 4).
  • f(x) = (x + 9)², x ≥ -9 has the inverse f⁻¹(x) = √x - 9, x ≥ 0.

Combining Functions to Find Inverses

  • Given f(x) = x + 5 and g(x) = 3x⁶, then f⁻¹(x) = x - 5, g⁻¹(x) = ⁶√(x/3), and (g⁻¹ o f⁻¹)(x) = ⁶√((x+5)/3).

Real-World Applications of Inverse Functions

  • For a business, the cost C to make personalized T-shirts is given by C(x) = 7.50x + 1500, where x represents the number of T-shirts.
  • C(x) represents the total cost of making x units of T-shirts, and C⁻¹(x) represents the number of T-shirts that can be made for a given total cost.

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