Composition of Functions - Worksheet 1

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Questions and Answers

What is the result of f(g(5)) if f(x)=4x+3 and g(x)=x-2?

15

What do you get when you calculate g(f(-6)) for f(x)=4x+3 and g(x)=x-2?

-23

What is the result of f(f(7)) if f(x)=4x+3?

127

What is the composition g(f(x)) if f(x)=4x+3 and g(x)=x-2?

<p>4x + 1</p> Signup and view all the answers

Calculate (fog)(x) if f(x)=6x^2 and g(x)=14x+4.

<p>1176x^2 + 672x + 48</p> Signup and view all the answers

What is the result of (gof)(x) for f(x)=6x^2 and g(x)=14x+4?

<p>84x^2 + 4</p> Signup and view all the answers

Are the results of g(f(-6)) and f(g(5)) the same?

<p>False (B)</p> Signup and view all the answers

Flashcards

f(g(x))

This involves substituting the entire function g(x) into the variable x of the function f(x).

g(f(x))

This involves substituting the entire function f(x) into the variable x of the function g(x).

Finding f(g(5))

To calculate f(g(5)), first evaluate g(5) using the function g(x)=x-2. Then plug the result into f(x)=4x+3.

Finding g(f(-6)).

To calculate g(f(-6)), first evaluate f(-6) using the function f(x)=4x+3. Then plug the result into g(x)=x-2.

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Finding f(f(7))

To calculate f(f(7)), first evaluate f(7) using the function f(x)=4x+3. Then plug the result into the same function f(x)=4x+3.

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Function Composition

This involves combining functions f(x) and g(x) in a specific order, where the output of the first function becomes the input of the second function.

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Composition (gof)(x)

In this case, you are substituting the entire function f(x) into the x of the function g(x).

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Study Notes

Composition of Functions

  • Function Definitions:

    • ( f(x) = 4x + 3 )
    • ( g(x) = x - 2 )
  • Example Calculation:

    • For ( f(g(5)) ):
      • Calculate ( g(5) = 5 - 2 = 3 )
      • Then ( f(3) = 4(3) + 3 = 15 )
  • Example Calculation:

    • For ( g(f(-6)) ):
      • Find ( f(-6) = 4(-6) + 3 = -21 )
      • Then ( g(-21) = -21 - 2 = -23 )
  • Example Calculation:

    • For ( f(f(7)) ):
      • Calculate ( f(7) = 4(7) + 3 = 31 )
      • Then ( f(31) = 4(31) + 3 = 127 )
  • Composite Function:

    • For ( g(f(x)) ):
      • Start with ( f(x) = 4x + 3 )
      • Then calculate ( g(4x + 3) = (4x + 3) - 2 = 4x + 1 )

Alternative Functions

  • Using Different Functions:

    • If ( f(x) = 6x^2 ) and ( g(x) = 14x + 4 ):
      • Composition ( (f \circ g)(x) ):
        • Calculate ( g(x) = 14x + 4 )
        • Then ( f(g(x)) = f(14x + 4) = 6(14x + 4)^2 = 1176x^2 + 672x + 48 )
  • Other Composition:

    • For ( (g \circ f)(x) ):
      • Start with ( f(x) = 6x^2 )
      • Then calculate ( g(f(x)) = g(6x^2) = 14(6x^2) + 4 = 84x^2 + 4 )

Key Observations

  • Difference in Results:
    • The results of ( (f \circ g)(x) ) and ( (g \circ f)(x) ) are not the same.
    • This demonstrates that function composition is not commutative; the order matters.
    • Understanding composition typically requires familiarity with the specific functions involved.

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