Math Problem Statement

For the function f : R → R defined by f (x) = 2 loge(2x − 1) + 4 (a) Find the domain of f (x). (b) Describe the full set of transformations, which when applied to the graph of y = loge(x) produces the graph of f .

Solution

Let's break this down step by step.

(a) Finding the domain of f(x)=2ln(2x1)+4f(x) = 2 \ln(2x - 1) + 4

The logarithmic function ln(x)\ln(x) (or loge(x)\log_e(x)) is only defined when its argument is positive, i.e., x>0x > 0.

For the function f(x)=2ln(2x1)+4f(x) = 2 \ln(2x - 1) + 4, we need the expression inside the logarithm, 2x12x - 1, to be greater than 0:

2x1>02x - 1 > 0

Solving this inequality:

2x>1x>122x > 1 \quad \Rightarrow \quad x > \frac{1}{2}

Thus, the domain of f(x)f(x) is:

x>12\boxed{x > \frac{1}{2}}

(b) Describing the transformations

The basic logarithmic function is y=ln(x)y = \ln(x), and we need to describe the transformations applied to this function to obtain f(x)=2ln(2x1)+4f(x) = 2 \ln(2x - 1) + 4.

Let’s identify each transformation step by step:

  1. Horizontal scaling:

    • The term ln(2x1)\ln(2x - 1) involves 2x12x - 1. First, consider the factor of 2 in front of xx. This causes a horizontal compression by a factor of 12\frac{1}{2} because for ln(kx)\ln(kx), the graph is compressed horizontally by kk.
  2. Horizontal translation:

    • The 1-1 in 2x12x - 1 indicates a horizontal shift to the right by 12\frac{1}{2}. This is because solving 2x1=02x - 1 = 0 gives x=12x = \frac{1}{2}, meaning the graph is shifted right by 12\frac{1}{2}.
  3. Vertical scaling:

    • The factor of 2 in front of ln(2x1)\ln(2x - 1) causes a vertical stretching of the graph by a factor of 2.
  4. Vertical translation:

    • The +4+4 at the end indicates a vertical shift upwards by 4 units.

Final set of transformations:

  • Horizontal compression by a factor of 12\frac{1}{2}.
  • Horizontal shift right by 12\frac{1}{2}.
  • Vertical stretch by a factor of 2.
  • Vertical shift up by 4 units.

These transformations, when applied to the graph of y=ln(x)y = \ln(x), result in the graph of f(x)=2ln(2x1)+4f(x) = 2 \ln(2x - 1) + 4.


Would you like further details or have any questions about these transformations? Here are 5 related questions you might find useful:

  1. How would you find the range of f(x)f(x)?
  2. What would be the effect on the domain if the constant inside the logarithm was different, say ln(3x1)\ln(3x - 1)?
  3. How would the transformations change if the function was 3ln(2x1)+23 \ln(2x - 1) + 2?
  4. Can you graph f(x)=2ln(2x1)+4f(x) = 2 \ln(2x - 1) + 4 and describe its key features (intercepts, asymptotes)?
  5. How would the graph behave as xx approaches infinity?

Tip: Always ensure the argument inside the logarithmic function is positive when finding domains involving logarithms.

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Math Problem Analysis

Mathematical Concepts

Logarithmic Functions
Domain of a Function
Graph Transformations

Formulas

f(x) = 2 ln(2x - 1) + 4
Domain of logarithmic function: x > 0

Theorems

Properties of logarithms
Transformations of functions

Suitable Grade Level

Grades 11-12