Chapter 5: Problem 55
Given that \(\log _{a} 2=0.301, \log _{a} 7=0.845,\) and \(\log _{a} 11=1.041,\) find each of the following, if possible. Round the answer to the nearest thousandth. $$\log _{a} 98$$
Short Answer
Expert verified
1.991
Step by step solution
01
Factorize the given number
Express 98 as a product of its prime factors. Notice that 98 = 2 × 7 × 7 (or 2 × 7^2).
02
Apply logarithm properties
Using the logarithm property \(\text{log}_a (x \times y) = \text{log}_a x + \text{log}_a y\), we can write \(\text{log}_a 98\) as \(\text{log}_a (2 \times 7^2)\).
03
Split the logarithms
Using the properties of logarithms, split \(\text{log}_a (2 \times 7^2)\) into \(\text{log}_a 2 + \text{log}_a 7^2\).
04
Apply the power rule
Using the power rule of logarithms \(\text{log}_a (y^k) = k \times \text{log}_a y\), rewrite \(\text{log}_a 7^2\) as \((2 \times \text{log}_a 7)\).
05
Substitute known values
Substitute the known values of \(\text{log}_a 2 = 0.301\) and \(\text{log}_a 7 = 0.845\) into the equation. You get \(\text{log}_a 2 + 2 \times \text{log}_a 7 = 0.301 + 2 \times 0.845\).
06
Perform the calculations
Complete the calculation \(\text{log}_a 98 = 0.301 + 2 \times 0.845 = 0.301 + 1.69 = 1.991\).
07
Round to the nearest thousandth
Round the result to the nearest thousandth. \(\text{log}_a 98 = 1.991\) is already rounded to the nearest thousandth.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
logarithm properties
Logarithms are a way to express exponentiation. They help in transforming multiplicative relationships into additive ones. The basic properties of logarithms simplify complex calculations. Here are some key properties:
- \text{Product Property}: \(\text{log}_a (xy) = \text{log}_a x + \text{log}_a y\) This property allows you to split the logarithm of a product into the sum of the logarithms of individual factors.
- \text{Quotient Property}: \(\text{log}_a (x/y) = \text{log}_a x - \text{log}_a y\) This property helps you break down the logarithm of a fraction.
- \text{Power Rule}: \(\text{log}_a (x^k) = k \times \text{log}_a x\) This property is useful for handling exponents inside a logarithm.
prime factorization
Prime factorization is the process of breaking down a composite number into its prime factors. Prime numbers are numbers greater than 1 that have no other divisors other than 1 and themselves.
For example, the prime factorization of 98 goes like this:
For example, the prime factorization of 98 goes like this:
- First, we divide 98 by the smallest prime number which is 2:$$ 98 \div 2 = 49$$Therefore, one factor is 2.
- Next, we recognize that 49 is not prime, so we continue dividing by the next smallest prime number, which is 7: $$ 49 = 7 \times 7$$
- So, we can say:$$ 98 = 2 \times 7^2$$
power rule of logarithms
The power rule of logarithms states that the logarithm of a number raised to an exponent can be expressed by multiplying the exponent by the logarithm of the base number. Mathematically, it is written as:
\text{log}_a (y^k) = k \times \text{log}_a y
This rule simplifies expressions where the argument of the logarithm is an exponential term. Here’s a step-by-step example:
\text{log}_a (y^k) = k \times \text{log}_a y
This rule simplifies expressions where the argument of the logarithm is an exponential term. Here’s a step-by-step example:
- Suppose you have \text{log}_a 7^2. Using the power rule:$$ \text{log}_a 7^2 = 2 \times \text{log}_a 7$$
- If \text{log}_a 7 is already known, say 0.845, then we substitute the value in:$$ 2 \times 0.845 = 1.69$$