Math Problem Statement

Find the function compositions for f(x) = 2x + 8 and g(x) = 4x - 8: a. (f ∘ g)(x), b. (g ∘ f)(x), c. (f ∘ g ∘ f)(x)

Solution

You provided two functions:

f(x)=2x+8f(x) = 2x + 8 g(x)=4x8g(x) = 4x - 8

The questions ask for compositions of these functions:

a. (fg)(x)(f \circ g)(x)

This is the composition of ff and gg, meaning we substitute g(x)g(x) into f(x)f(x).

(fg)(x)=f(g(x))=f(4x8)(f \circ g)(x) = f(g(x)) = f(4x - 8) Substitute 4x84x - 8 into f(x)f(x):

f(4x8)=2(4x8)+8f(4x - 8) = 2(4x - 8) + 8 Simplify: =8x16+8=8x8= 8x - 16 + 8 = 8x - 8 So: (fg)(x)=8x8(f \circ g)(x) = 8x - 8

b. (gf)(x)(g \circ f)(x)

This is the composition of gg and ff, meaning we substitute f(x)f(x) into g(x)g(x).

(gf)(x)=g(f(x))=g(2x+8)(g \circ f)(x) = g(f(x)) = g(2x + 8) Substitute 2x+82x + 8 into g(x)g(x):

g(2x+8)=4(2x+8)8g(2x + 8) = 4(2x + 8) - 8 Simplify: =8x+328=8x+24= 8x + 32 - 8 = 8x + 24 So: (gf)(x)=8x+24(g \circ f)(x) = 8x + 24

c. (fgf)(x)(f \circ g \circ f)(x)

This is a composition of ff, gg, and ff, meaning we first find f(x)f(x), then g(f(x))g(f(x)), and finally f(g(f(x)))f(g(f(x))).

From part (b), we already know that: (gf)(x)=8x+24(g \circ f)(x) = 8x + 24 Now substitute 8x+248x + 24 into f(x)f(x):

f(8x+24)=2(8x+24)+8f(8x + 24) = 2(8x + 24) + 8 Simplify: =16x+48+8=16x+56= 16x + 48 + 8 = 16x + 56 So: (fgf)(x)=16x+56(f \circ g \circ f)(x) = 16x + 56

Summary of Results:

  • (fg)(x)=8x8(f \circ g)(x) = 8x - 8
  • (gf)(x)=8x+24(g \circ f)(x) = 8x + 24
  • (fgf)(x)=16x+56(f \circ g \circ f)(x) = 16x + 56

Would you like more details on these compositions or have any questions?

Here are 5 follow-up questions for practice:

  1. How would the results change if f(x)=3x+5f(x) = 3x + 5 and g(x)=x4g(x) = x - 4?
  2. What is the inverse of f(x)=2x+8f(x) = 2x + 8?
  3. How would you graph (fg)(x)(f \circ g)(x)?
  4. What are the domains of f(x)f(x), g(x)g(x), and their compositions?
  5. Can you find (gfg)(x)(g \circ f \circ g)(x)?

Tip: When solving function compositions, always start from the innermost function and work your way outward.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Algebra

Formulas

(f ∘ g)(x) = f(g(x))
(g ∘ f)(x) = g(f(x))
(f ∘ g ∘ f)(x) = f(g(f(x)))

Theorems

Basic Function Composition Rules

Suitable Grade Level

Grades 10-12