Chapter 10: Problem 32
Use a calculator to approximate each logarithm to four decimal places. $$\log _{2} 15$$
Short Answer
Expert verified
\(\text{log}_{2} 15 \approx 3.9069\)
Step by step solution
01
Understanding the Logarithm
The exercise asks to approximate \(\text{log}_{2} 15\) to four decimal places. This means finding the exponent to which 2 must be raised to obtain 15.
02
Change of Base Formula
Use the change of base formula for logarithms: \(\text{log}_{b} a = \frac{\text{log} a}{\text{log} b}\). This allows the logarithm to be converted to base 10, which can be used with a calculator.
03
Apply the Formula
Apply the change of base formula with \(\text{log}_{2} 15\): \(\text{log}_{2} 15 = \frac{\text{log} 15}{\text{log} 2}\).
04
Use a Calculator
Use the calculator to find \(\text{log} 15\) and \(\text{log} 2\): \(\text{log} 15 \approx 1.1761\) and \(\text{log} 2 \approx 0.3010\).
05
Calculate the Result
Divide the results from Step 4: \(\frac{1.1761}{0.3010} \approx 3.9069\).
06
Round to Four Decimal Places
Ensure the result is rounded to four decimal places. The computed value \(\text{log}_{2} 15 \approx 3.9069\) is already to four decimal places.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Change of Base Formula
The change of base formula is a very useful tool in mathematics. It allows us to convert logarithms from one base to another, making it easier to use a calculator for the calculations. The formula is defined as: \[ \log_b a = \frac{\log a}{\log b} \]Here, \( \log b \) represents the logarithm of the base to which we want to convert. For example, if you want to calculate \( \log_2 15 \), you can convert it into a base-10 logarithm (which is commonly available on calculators) using the change of base formula: \[ \log_2 15 = \frac{\log 15}{\log 2} \] By transforming the base, the computation of non-standard logarithms becomes straightforward and convenient.
Logarithmic Functions
Logarithmic functions are the inverse of exponential functions. In simpler terms, if you have an equation \( y = b^x \), then its logarithmic form would be \( x = \log_b y \). The logarithm \( \log_b y \) answers the question: **To what power must the base \( b \) be raised to produce the number \( y \)?** Logarithms have several properties that make them extremely useful in mathematics:
- The product rule: \( \log_b (MN) = \log_b M + \log_b N \)
- The quotient rule: \( \log_b \left( \frac{M}{N} \right) = \log_b M - \log_b N \)
- The power rule: \( \log_b (M^p) = p \cdot \log_b M \)
Using a Calculator for Logarithms
Calculators are handy tools for quickly computing logarithms, especially those with base-10 (common logarithms) and base-e (natural logarithms). When using a calculator to find logarithms, simply follow these steps:
- Identify the logarithm you need to compute. For example, \( \log_2 15 \).
- Convert the original base to base-10 using the change of base formula: \( \log_2 15 = \frac{\log 15}{\log 2} \).
- Use the calculator to find \( \log 15 \) and \( \log 2 \). Once you input these values, you can get the approximate values: \( \log 15 \approx 1.1761 \) and \( \log 2 \approx 0.3010 \).
- Divide the results from the calculator: \( \frac{1.1761}{0.3010} \approx 3.9069 \).
- Round the final result to the required number of decimal places. In this case, 4 decimal places: \( 3.9069 \).