Chapter 1: Problem 269
For the following exercises, sketch the graph of the logarithmic function. Determine the domain, range, and vertical asymptote. $$ f(x)=\ln (x+1) $$
Short Answer
Expert verified
Domain: \((-1, \infty)\), Range: \((-\infty, \infty)\), Vertical Asymptote: \(x=-1\).
Step by step solution
01
Identify the Parent Function
The given function is a natural logarithm function, represented as \( f(x) = \ln(x+1) \). The parent function for a natural logarithm is \( f(x) = \ln x \). This information helps in understanding how the shift affects the graph.
02
Determine Horizontal Shift
The function \( \ln(x+1) \) indicates a horizontal shift. For the two logarithmic expressions \( f(x) = \ln(x) \) and \( f(x) = \ln(x+1) \), the term \(+1\) inside the logarithm implies the graph is shifted 1 unit left on the x-axis.
03
Identify the Domain of the Funct ion
For the function \( \ln(x+1) \), we need \( x+1 > 0 \) for the logarithm to be defined, which simplifies to \( x > -1 \). Hence, the domain of the function is \( x \in (-1, \infty) \).
04
Identify the Range of the Function
The range of a logarithmic function is all real numbers, \( (-\infty, \infty) \), because as \( x \) approaches infinity, the log function increases without bound, and as \( x \) approaches -1 from the right, the log function approaches negative infinity.
05
Determine the Vertical Asymptote
Vertical asymptotes for logarithmic functions occur where the argument of the logarithm is zero. Solving \( x+1=0 \) gives \( x = -1 \) as the point for the vertical asymptote.
06
Sketch the Graph
Begin by drawing the vertical asymptote line at \( x = -1 \). Mark the domain \( x > -1 \). The graph starts near negative infinity as \( x \) approaches -1 from the right, and it rises gradually without bound as \( x \) increases. Sketch this curve carefully, reflecting the characteristics of the natural logarithm with the specified horizontal shift.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Natural Logarithm
The natural logarithm is a specifically significant logarithmic function denoted as \( \ln(x) \). Unlike other logarithms, it has a base of \( e \), an irrational constant approximately equal to 2.718. Natural logarithms are widely used due to their natural properties, mostly in calculus and natural growth models.
- They convert multiplication into addition, simplifying calculations involving exponential functions.
- In the function \( f(x) = \ln(x) \), \( x \) must be greater than zero, as log of zero or negative numbers is undefined.
Horizontal Shift
When you encounter expressions like \( f(x) = \ln(x+1) \), it signals a horizontal shift of the graph on the x-axis. Understanding Horizontal Shifts:
- If \( x \) is replaced by \( x + c \), where \( c \) is a constant, the graph shifts \( c \) units to the left.
- If \( x \) is replaced by \( x - c \), the graph shifts \( c \) units to the right.
Domain and Range
Determining the domain and range of a function helps in understanding where the function is defined and what values it can take. Domain: For the function \( f(x) = \ln(x+1) \), the expression inside the logarithm, \( x+1 \), must be greater than zero. This translates to:
- Solving the inequality \( x+1 > 0 \) gives \( x > -1 \).
- Therefore, the domain is \( x \in (-1, \infty) \).
- As \( x \) approaches infinity, \( \ln(x+1) \) increases without bound.
- As it approaches the boundary of the domain from the right, the log value approaches negative infinity.
- Consequently, the range is \( (-\infty, \infty) \).
Vertical Asymptote
A vertical asymptote is a vertical line that indicates where a function’s graph might tend towards infinity, but never actually touches or crosses. In our logarithmic function \( \ln(x+1) \), determining the vertical asymptote involves finding when \( x+1 \) equals zero. Identifying Vertical Asymptote:
- Set the expression inside the logarithm equal to zero: \( x+1=0 \).
- This gives \( x = -1 \) as the equation of the vertical asymptote.