Math Problem Statement

Suppose f(x) = x + 2, g(x) = x - 2, and h(x) = 3x for x ∈ R, where R is the set of real numbers. Find (g ∘ f), (f ∘ g), (f ∘ f), and (g ∘ g).

Solution

To solve this problem, we compute the compositions of the given functions f(x)=x+2f(x) = x+2, g(x)=x2g(x) = x-2, and h(x)=3xh(x) = 3x as specified. Let’s calculate each step by step:


1. Compute (gf)(x)(g \circ f)(x):

This means g(f(x))g(f(x)), so substitute f(x)=x+2f(x) = x+2 into g(x)=x2g(x) = x-2:

g(f(x))=g(x+2)=(x+2)2=x.g(f(x)) = g(x+2) = (x+2) - 2 = x.

Thus, (gf)(x)=x(g \circ f)(x) = x.


2. Compute (fg)(x)(f \circ g)(x):

This means f(g(x))f(g(x)), so substitute g(x)=x2g(x) = x-2 into f(x)=x+2f(x) = x+2:

f(g(x))=f(x2)=(x2)+2=x.f(g(x)) = f(x-2) = (x-2) + 2 = x.

Thus, (fg)(x)=x(f \circ g)(x) = x.


3. Compute (ff)(x)(f \circ f)(x):

This means f(f(x))f(f(x)), so substitute f(x)=x+2f(x) = x+2 into itself:

f(f(x))=f(x+2)=(x+2)+2=x+4.f(f(x)) = f(x+2) = (x+2) + 2 = x + 4.

Thus, (ff)(x)=x+4(f \circ f)(x) = x + 4.


4. Compute (gg)(x)(g \circ g)(x):

This means g(g(x))g(g(x)), so substitute g(x)=x2g(x) = x-2 into itself:

g(g(x))=g(x2)=(x2)2=x4.g(g(x)) = g(x-2) = (x-2) - 2 = x - 4.

Thus, (gg)(x)=x4(g \circ g)(x) = x - 4.


Final Results:

  1. (gf)(x)=x(g \circ f)(x) = x
  2. (fg)(x)=x(f \circ g)(x) = x
  3. (ff)(x)=x+4(f \circ f)(x) = x + 4
  4. (gg)(x)=x4(g \circ g)(x) = x - 4

Would you like a detailed explanation of any of these calculations?


5 Related Questions:

  1. What are the properties of composition functions such as fgf \circ g and gfg \circ f?
  2. How does the identity function relate to the compositions (gf)(x)=x(g \circ f)(x) = x and (fg)(x)=x(f \circ g)(x) = x?
  3. Can we compute higher-order compositions, such as (fff)(x)(f \circ f \circ f)(x)?
  4. What happens if we compose h(x)h(x) with f(x)f(x) or g(x)g(x)?
  5. How do these compositions affect the domain and range of the resulting functions?

Tip:

Always evaluate the inner function first when working with compositions. This ensures accuracy and clarity in computations.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Linear Functions
Algebra

Formulas

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

Theorems

Function Composition Properties

Suitable Grade Level

Grades 10-12