Math Problem Statement

Diketahui fungsi f(x) = (x - 4)/(4 - x) dan g(x) = 2x - 5. Fungsi invers dari (g o f)(x) adalah?

Solution

We are given two functions, f(x)=x44xf(x) = \frac{x - 4}{4 - x} and g(x)=2x5g(x) = 2x - 5, and the task is to find the inverse of (gf)(x)(g \circ f)(x), which is the composition of the functions g(f(x))g(f(x)).

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

The composition g(f(x))g(f(x)) means applying gg to the result of f(x)f(x). So, substitute f(x)f(x) into g(x)g(x): g(f(x))=g(x44x)g(f(x)) = g\left(\frac{x - 4}{4 - x}\right) Since g(x)=2x5g(x) = 2x - 5, replace xx with x44x\frac{x - 4}{4 - x}: g(f(x))=2(x44x)5g(f(x)) = 2\left(\frac{x - 4}{4 - x}\right) - 5 Now simplify this expression: g(f(x))=2(x4)4x5g(f(x)) = \frac{2(x - 4)}{4 - x} - 5 The first term becomes: 2(x4)4x=2x84x\frac{2(x - 4)}{4 - x} = \frac{2x - 8}{4 - x} Thus: g(f(x))=2x84x5g(f(x)) = \frac{2x - 8}{4 - x} - 5 Convert 5-5 to a fraction with the same denominator: g(f(x))=2x84x5(4x)4x=2x820+5x4xg(f(x)) = \frac{2x - 8}{4 - x} - \frac{5(4 - x)}{4 - x} = \frac{2x - 8 - 20 + 5x}{4 - x} Simplify the numerator: g(f(x))=7x284xg(f(x)) = \frac{7x - 28}{4 - x}

Step 2: Find the Inverse of g(f(x))g(f(x))

To find the inverse of g(f(x))g(f(x)), set y=7x284xy = \frac{7x - 28}{4 - x} and solve for xx in terms of yy: y(4x)=7x28y(4 - x) = 7x - 28 Expand both sides: 4yyx=7x284y - yx = 7x - 28 Collect all terms involving xx on one side: 4y+28=7x+yx4y + 28 = 7x + yx Factor xx on the right-hand side: 4y+28=x(7+y)4y + 28 = x(7 + y) Solve for xx: x=4y+287+yx = \frac{4y + 28}{7 + y}

Step 3: Verify the Answer

This expression matches option A: 7x+28x+4\frac{7x + 28}{x + 4}

Thus, the correct answer is A.


Would you like more details or explanations about any step? Here are some related questions you could explore:

  1. What is the domain of the function f(x)f(x)?
  2. How do you verify if a function is invertible?
  3. What is the graphical interpretation of the inverse function?
  4. How can we simplify complex fractions in function compositions?
  5. What are the properties of composite functions?

Tip: When solving for the inverse of a function, always remember to express the original variable xx in terms of the new variable yy, and then swap them to finalize the inverse.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Composite Functions
Inverse Functions
Algebra

Formulas

f(x) = (x - 4)/(4 - x)
g(x) = 2x - 5
g(f(x)) = 2[(x - 4)/(4 - x)] - 5

Theorems

Inverse Function Theorem
Function Composition

Suitable Grade Level

Grades 10-12