Chapter 4: Problem 42
Exer. 35-46: Sketch the graph of \(f\) $$f(x)=\log _{3}\left(x^{3}\right)$$
Short Answer
Expert verified
The graph of \( f(x) = \log_3(x^3) \) is a steeper version of \( \log_3(x) \) with key point (1,0).
Step by step solution
01
Understand the Function
The function given is \( f(x) = \log_3(x^3) \). We need to understand its components. Notice that \( \log_3(x^3) \) can be rewritten using logarithm properties as \( 3 \cdot \log_3(x) \). This shows the function is a vertical stretch of \( \log_3(x) \) by a factor of 3.
02
Identify Domain and Range
The domain of the function \( f(x) = \log_3(x^3) \) is all positive \( x \) since \( x^3 \) must be greater than 0 for the logarithm to be defined. Thus, the domain is \( x > 0 \). The range of a logarithmic function, even when transformed, is all real numbers \( \mathbb{R} \).
03
Calculate Key Points
To help sketch the graph, calculate some key points. For simplicity, let's use \( x = 1, 3, 9 \). \( f(1) = \log_3(1^3) = \log_3(1) = 0 \). \( f(3) = \log_3(3^3) = \log_3(27) = 3 \). \( f(9) = \log_3(9^3) = \log_3(729) \). These points give a sense of the shape.
04
Sketch General Shape of Logarithmic Functions
Sketch the basic graph of \( \log_3(x) \), which passes through the point \((1, 0)\) and rises slowly to the right. Since our function is \( 3 \cdot \log_3(x) \), this graph will be steeper as it stretches vertically by a factor of 3.
05
Plot Calculated Points and Shape
Plot the key points from Step 3: \((1,0), (3,3)\) and assume the value for \((9, f(9))\) using a calculator if needed for precision. Draw a smooth curve through these points following the vertical stretch from the basic shape of \( \log_3(x) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Graph Sketching
Sketching the graph of a logarithmic function like \( f(x) = \log_3(x^3) \) involves understanding how transformations affect the basic shape of the logarithmic graph. Begin by considering the basic graph of \( \log_3(x) \), which typically looks like a slowly rising curve that passes through the point \((1, 0)\). To sketch \( \log_3(x^3) \), first notice how it can be rewritten as \( 3 \cdot \log_3(x) \). This transforms the graph by stretching it vertically by a factor of 3. Each \( y \)-value on the basic log graph is multiplied by 3, resulting in a steeper ascent.
- Start your graph at \((1, 0)\) because any logarithm of 1 is 0, regardless of its base.
- Then smoothly and steeply rise to the right, depicting a steeper than usual growth due to the multiplier 3.
- Key points to plot might include \((3, 3)\) reflecting the logarithmic base 3 raised cubed to give 27, re-evaluating as 3.
Function Domain
Understanding the domain of a logarithmic function is a vital part of solving these problems. The domain of \( f(x) = \log_3(x^3) \) requires the argument of the logarithm, \( x^3 \), to be positive because logarithms of non-positive numbers are undefined. Given this requirement:
- The function's domain is all positive \( x \) values, or \( x > 0 \).
Logarithm Properties
Logarithm properties simplify working with more complex logarithmic functions and enhance comprehension. For the function \( f(x) = \log_3(x^3) \), we use the property that allows for the exponent to come in front of the logarithm: \( \log_b(a^c) = c \cdot \log_b(a) \). This means \( \log_3(x^3) \) can be rewritten as \( 3 \cdot \log_3(x) \).
- This simplifies calculations and interpretation of transformations, showing the function is a vertically stretched version of \( \log_3(x) \).
- Recognizing this property facilitates identifying graph behaviors and domain impacts.
- Understanding this shift enhances strategic plotting of key points like \((1,0)\), \((3,3)\), and enables accuracy in depicting steeper growth.