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Verifying inverse functions by composition

Verifying inverse functions by composition

Verifying inverse functions by composition involves checking if two functions are inverses of each other by composing them. For two functions f(x)f(x) and g(x)g(x) to be inverses, the following conditions must hold:

  1. Composition in one direction: f(g(x))=xf(g(x)) = x for all xx in the domain of gg.
  2. Composition in the reverse direction: g(f(x))=xg(f(x)) = x for all xx in the domain of ff.

If both conditions are satisfied, then ff and gg are indeed inverse functions of each other. This method provides a systematic way to confirm the relationship between two functions.

Part 1: Verifying inverse functions from tables

Inverse functions undo each other. Functions s and t are inverses if and only if s(t(x))=x and t(s(x))=x for every x-value in the domains.

When studying "Verifying inverse functions from tables," focus on these key points:

  1. Definition of Inverse Functions: Understand that if f(x)f(x) is a function, its inverse f1(x)f^{-1}(x) swaps the original input and output.

  2. Finding Values: For each pair in the original function table, look for the corresponding output in the inverse function table.

  3. Verification Process: To verify that two functions are inverses, check that:

    • f(f1(x))=xf(f^{-1}(x)) = x
    • f1(f(x))=xf^{-1}(f(x)) = x
  4. Table Relationships: Ensure that each output value in the original table matches an input value in the inverse table, and vice versa.

  5. Symmetry in Points: Recognize that the points (a,b)(a, b) in the original function correspond to (b,a)(b, a) in the inverse function.

  6. Order of Operations: Confirm that for every value that retrieves the original pairs through the function and its inverse, the operations yield consistent results.

By focusing on these aspects, you can effectively verify and understand inverse functions using tables.

Part 2: Using specific values to test for inverses

Are two functions inverses? Even one counterexample can show that they are not. How many examples would it take to show that they really are inverses?

When studying "Using Specific Values to Test for Inverses," focus on these key points:

  1. Definition of Inverse Functions: Understand that if ff is a function and f1f^{-1} is its inverse, then f(f1(x))=xf(f^{-1}(x)) = x and f1(f(x))=xf^{-1}(f(x)) = x for all xx in the domain.

  2. Choosing Specific Values: Select specific input values for xx in the function f(x)f(x) and compute ff and f1f^{-1} to check if they return the initial input.

  3. Verification Process: For a given function ff:

    • Calculate y=f(x)y = f(x).
    • Use yy as input in f1(y)f^{-1}(y).
    • Check if the result equals xx.
  4. Graphical Interpretation: Understand that the graphs of a function and its inverse are reflections over the line y=xy = x.

  5. Domain and Range Considerations: Recognize that the domain of ff becomes the range of f1f^{-1} and vice versa.

  6. Function Characteristics: Ensure that the function is one-to-one (bijective), as only one-to-one functions have inverses.

By focusing on these areas, you can effectively test and understand inverses using specific values.

Part 3: Verifying inverse functions by composition

Sal composes f(x)=(x+7)³-1 and g(x)=∛(x+1)-7, and finds that f(g(x))=g(f(x))=x, which means the functions are inverses!

Here are the key points to learn when studying "Verifying inverse functions by composition":

  1. Definition of Inverse Functions: For two functions f(x)f(x) and g(x)g(x), gg is the inverse of ff if f(g(x))=xf(g(x)) = x and g(f(x))=xg(f(x)) = x for all xx in the domain of gg and ff, respectively.

  2. Composition of Functions: Understand how to compose functions. The composition f(g(x))f(g(x)) means applying gg first and then applying ff to the result.

  3. Checking Inverses:

    • To verify that gg is the inverse of ff:
      • Calculate f(g(x))f(g(x)) and check if it equals xx.
      • Calculate g(f(x))g(f(x)) and check if it equals xx.
  4. Domain and Range Considerations: Be aware of the domains and ranges of the functions involved, as they determine valid inputs and outputs.

  5. One-to-One Function Requirement: Recognize that for a function to have an inverse, it must be one-to-one (each output is produced by exactly one input).

  6. Graphical Understanding: The graphs of a function and its inverse are reflections across the line y=xy = x.

  7. Algebraic Techniques: Familiarize yourself with algebraic methods for finding inverses, including solving for yy and swapping variables.

  8. Examples and Practice: Work through several examples to solidify understanding of how to determine and verify inverse functions.

By mastering these points, you will be able to effectively verify if two functions are inverses of each other through composition.

Part 4: Verifying inverse functions by composition: not inverse

Sal composes f(x)=2x-3 and g(x)=½x+3, and finds that f(g(x)) ≠ g(f(x)) ≠ x, which means the functions are not inverses.

When studying "Verifying Inverse Functions by Composition: Not Inverse," focus on these key points:

  1. Definition of Inverse Functions: Two functions f(x)f(x) and g(x)g(x) are inverses if f(g(x))=xf(g(x)) = x and g(f(x))=xg(f(x)) = x.

  2. Composition: To verify inverse functions, compute the composition f(g(x))f(g(x)) and g(f(x))g(f(x)).

  3. Not Inverse Functions: If either composition does not equal xx, the functions are not inverses.

  4. Counterexamples: Provide examples of functions where the compositions do not yield xx to illustrate that they are not inverses.

  5. Finding Inverses: If the functions are not inverses, explore methods to determine their actual inverses where applicable.

  6. Graphical Perspective: Recognize that inverse functions can often be understood visually by checking if the graphs are symmetric about the line y=xy = x.

By mastering these points, you'll understand how to verify whether functions are inverses and what it means when they are not.