Chapter 10: Problem 185
In the following exercises, graph each logarithmic function. \(y=\log _{\frac{1}{5}} x\)
Short Answer
Expert verified
Plot points \((1, 0)\), \((\frac{1}{5}, 1)\), and \((5, -1)\). Draw the curve through these points.
Step by step solution
01
Understand the function
The function given is a logarithmic function of the form \(y = \log _{ \frac{1}{5}} x\). Here, the base of the logarithm is \( \frac{1}{5}\).
02
Identify key points
Key points for graphing logarithmic functions are generally found by using simple values for \(x\) that make the logarithm easier to evaluate. Start with values like \(x = 1, x = \frac{1}{5}, x = 5\).
03
Calculate the key points
For \(x = 1\), \(y = \log _{\frac{1}{5}} 1 = 0\). For \(x = \frac{1}{5}\), \(y = \log _{\frac{1}{5}} \frac{1}{5} = 1\). For \(x = 5\), \(y = \log _{\frac{1}{5}} 5 = -1\).
04
Plot the points
Plot the points \((1, 0)\), \((\frac{1}{5}, 1)\), and \((5, -1)\) on the graph.
05
Draw the curve
Draw a smooth curve through these points. Remember that the graph of a logarithmic function approaches the y-axis (vertical asymptote) but never touches it.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
logarithmic function
A logarithmic function is an inverse of an exponential function. If you understand exponents, then you are already halfway to understanding logarithms. In a logarithmic function of the form \( y = \log_{b} x \), the base \( b \) is always a positive number, not equal to one, and \( x \) is a positive number. For example, \( y = \log_{\frac{1}{5}} x \) means we're looking for a number \( y \) such that \( (\frac{1}{5})^y = x \). For every positive \( x \), there's a corresponding \( y \) value that satisfies this equation.
graphing techniques
When graphing logarithmic functions, it's essential to identify some key points that belong to the function. Start by picking points for \( x \) that make the logarithm calculations simple. Typical key points include 1, the base \( b \), and the reciprocal of the base \( \frac{1}{b} \). For example, with the function \( y = \log_{\frac{1}{5}} x \), you would choose \( x = 1 \), \( x = 5 \), and \( x = \frac{1}{5} \). Then, calculate the corresponding \( y \) values:
- For \( x = 1 \), \( y = \log_{\frac{1}{5}} 1 = 0 \).
- For \( x = \frac{1}{5} \), \( y = \log_{\frac{1}{5}} \frac{1}{5} = 1 \).
- For \( x = 5 \), \( y = \log_{\frac{1}{5}} 5 = -1 \).
logarithm properties
Understanding the properties of logarithms can make graphing and manipulating these functions easier. Some critical properties are:
- \( \log_b 1 = 0 \) for any base \( b \), because any number raised to the power of 0 is 1.
- \( \log_b b = 1 \), reflecting that raising the base \( b \) to the power of 1 returns \( b \).
- Logarithms convert multiplication into addition: \( \log_b (xy) = \log_b x + \log_b y \).
- Logarithms convert division into subtraction: \( \log_b \left( \frac{x}{y} \right) = \log_b x - \log_b y \).
- Exponents inside the log can be moved to the front: \( \log_b (x^k) = k \log_b x \).
vertical asymptote
One crucial feature of the graph of a logarithmic function is the vertical asymptote. This is a line that the graph approaches but never touches or crosses. For \( y = \log_b x \), the vertical asymptote is at \( x = 0 \). This happens because logarithmic functions are undefined for non-positive values of \( x \). For example, in the function \( y = \log_{\frac{1}{5}} x \), as \( x \) gets closer to 0 from the right, \( y \) decreases without bound (\( y \) approaches negative infinity). Knowing the location of the vertical asymptote helps you sketch the graph more accurately by ensuring the curve approaches but does not cross the \( y \)-axis.