Math Problem Statement

Given the following functions, use function composition to determine if f(x) = -4x + 8 and g(x) = (x + 10) / -4 are inverse functions.

Solution

To determine whether f(x)=4x+8f(x) = -4x + 8 and g(x)=x+104g(x) = \frac{x + 10}{-4} are inverse functions, we need to use function composition. Specifically, we calculate:

  1. (fg)(x)(f \circ g)(x), which means substituting g(x)g(x) into f(x)f(x).
  2. (gf)(x)(g \circ f)(x), which means substituting f(x)f(x) into g(x)g(x).

Step 1: Compute (fg)(x)(f \circ g)(x)

Substitute g(x)=x+104g(x) = \frac{x + 10}{-4} into f(x)f(x): f(g(x))=f(x+104)=4(x+104)+8.f(g(x)) = f\left(\frac{x + 10}{-4}\right) = -4\left(\frac{x + 10}{-4}\right) + 8. Simplify: f(g(x))=(4)x+104+8=(x+10)+8=x+18.f(g(x)) = (-4) \cdot \frac{x + 10}{-4} + 8 = (x + 10) + 8 = x + 18.

Step 2: Compute (gf)(x)(g \circ f)(x)

Substitute f(x)=4x+8f(x) = -4x + 8 into g(x)g(x): g(f(x))=g(4x+8)=(4x+8)+104.g(f(x)) = g(-4x + 8) = \frac{(-4x + 8) + 10}{-4}. Simplify: g(f(x))=4x+184=x184=x184.g(f(x)) = \frac{-4x + 18}{-4} = x - \frac{18}{-4} = x - \frac{18}{-4}.

To verify whether f(x) = -4x + 8 } andLet's continue the process more cleanly. The question is whether \(f(x) = -4x + 8 and g(x)=x+104g(x) = \frac{x + 10}{-4} are inverses.

We already began the process of composition:

Step 1: Compute f(g(x))f(g(x))

Substituting g(x)=x+104g(x) = \frac{x + 10}{-4} into f(x)=4x+8f(x) = -4x + 8: f(g(x))=f(x+104)=4(x+104)+8.f(g(x)) = f\left(\frac{x + 10}{-4}\right) = -4\left(\frac{x + 10}{-4}\right) + 8. Simplify: f(g(x))=x+10+8=x+18.f(g(x)) = x + 10 + 8 = x + 18. Thus, f(g(x))=x+18f(g(x)) = x + 18, which is not equal to xx.

Step 2: Compute g(f(x))g(f(x))

Substitute f(x)=4x+8f(x) = -4x + 8 into g(x)=x+104g(x) = \frac{x + 10}{-4}: g(f(x))=g(4x+8)=(4x+8)+104.g(f(x)) = g(-4x + 8) = \frac{(-4x + 8) + 10}{-4}. Simplify: g(f(x))=4x+184=x184.g(f(x)) = \frac{-4x + 18}{-4} = x - \frac{18}{-4}. Simplify further: g(f(x))=x+4.5.g(f(x)) = x + 4.5. Thus, g(f(x))=x+4.5g(f(x)) = x + 4.5, which is not equal to xx.

Conclusion:

Since f(g(x))xf(g(x)) \neq x and g(f(x))xg(f(x)) \neq x, the functions f(x)f(x) and g(x)g(x) are not inverses.


Would you like further clarification?

Here are some related questions to expand understanding:

  1. How do you formally prove two functions are inverses?
  2. Can you find the inverse of f(x)=4x+8f(x) = -4x + 8 directly?
  3. What properties must a function have to possess an inverse?
  4. Why does function composition reveal whether functions are inverses?
  5. How does graphing help visualize inverse functions?

Tip: Always verify both f(g(x))=xf(g(x)) = x and g(f(x))=xg(f(x)) = x when checking for inverse relationships!

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Math Problem Analysis

Mathematical Concepts

Algebra
Function Composition
Inverse Functions

Formulas

f(g(x)) = f(g(x))
g(f(x)) = g(f(x))
If f(g(x)) = x and g(f(x)) = x, then f(x) and g(x) are inverses.

Theorems

Property of Inverse Functions

Suitable Grade Level

Grades 9-12