Logarithm Rules Practice Problems - Master Log Laws
Practice logarithmic laws with step-by-step solutions. Master product, quotient, power rules, change of base formula, and natural logarithms through targeted exercises.
Use quotient rule: log_a(M/N) = log_a(M) - log_a(N) for division inside logs
Master power rule: log_a(M^n) = n·log_a(M) to simplify exponential expressions
Convert between bases using change of base formula: log_b(x) = log_c(x)/log_c(b)
Solve logarithmic equations by converting to exponential form
Work with natural logarithms (ln) and understand e as the base
Understanding Rules of Logarithms
Complete explanation with examples
What Are Logarithmic Laws?
There are a few logarithmic laws worth knowing to make solving problems easier. The following laws are the main rules you will use. It should be noted that the letters a, m, n must be positive real numbers for these laws to be valid.
Step 1: Identify the property of logarithms that relates inverses.
Step 2: Apply this property to the given expression.
Step 3: Compare with provided choices to identify the correct option.
Now, let's work through each step:
Step 1: The problem asks us to find the expression equal to log491.
Step 2: We use the logarithmic property logba=logab1. Thus, replacing b with 9 and a with 4, we have:
log491=log94.
Step 3: Comparing this result to the provided choices, we find that the correct answer is log94, corresponding to Choice 1.
Therefore, the solution to the problem is log94.
Answer:
log94
Video Solution
Exercise #2
2log38=
Step-by-Step Solution
To solve this problem, let's simplify 2log38 using logarithm rules.
Step 1: Recognize the expression form The expression is of the form a⋅logbc, where a=2, b=3, and c=8.
Step 2: Apply the power property According to the power property of logarithms, 2⋅log38 can be simplified to log3(82).
Perform the calculation Calculate 82, which is 64.
Step 3: Simplify further Therefore, we have log364.
This is a straightforward application of the power property of logarithms. By applying this property correctly, we've simplified the original expression correctly.
Therefore, the simplified form of 2log38 is log364.
Answer:
log364
Video Solution
Exercise #3
log103+log104=
Step-by-Step Solution
To solve this problem, we will use the property of logarithms that allows us to combine the sum of two logarithms:
Step 1: Identify the formula. We use the property logb(x)+logb(y)=logb(x⋅y) where both logarithms must have the same base.
Step 2: Recognize the base. Here, both logarithms are in base 10: log103 and log104.
Step 3: Apply the property. Add the two logarithms using the formula: log103+log104=log10(3⋅4).
Step 4: Perform the multiplication. Compute 3⋅4 to get 12.
Step 5: Express the result as a single logarithm: log1012.
Therefore, the expression log103+log104 simplifies to log1012.
Answer:
log1012
Video Solution
Exercise #4
log24+log25=
Step-by-Step Solution
To solve this problem, we'll follow these steps:
Step 1: Identify the given expression as log24+log25.
Step 2: Use the sum of logarithms rule to simplify the expression.
Step 3: Calculate the product and express the result.
Let's work through each step:
Step 1: We have log24+log25 as our expression.
Step 2: Apply the sum of logarithms formula:
log24+log25=log2(4⋅5)
Step 3: Calculate the product:
4×5=20
Thus, log2(4⋅5)=log220.
Therefore, the solution to the problem is log220.
Answer:
log220
Video Solution
Exercise #5
log29−log23=
Step-by-Step Solution
To solve the problem of evaluating log29−log23, we apply the properties of logarithms as follows:
Step 1: Recognize that the expression uses a subtraction of logarithms with the same base: log29−log23.
Step 2: Use the logarithmic subtraction rule: logbA−logbB=logb(BA).
Step 3: Simplify using this rule: log29−log23=log2(39).
Step 4: Perform the division: 39=3.
Step 5: Therefore, log2(39)=log23.
Thus, the simplified and evaluated result is log23.
Answer:
log23
Video Solution
Frequently Asked Questions
Everything you need to know about Rules of Logarithms
What are the basic logarithm rules I need to memorize?
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The essential logarithm rules are: log_a(1) = 0, log_a(a) = 1, log_a(MN) = log_a(M) + log_a(N), log_a(M/N) = log_a(M) - log_a(N), and log_a(M^n) = n·log_a(M). These five rules form the foundation for solving most logarithmic problems.
How do I solve logarithmic equations step by step?
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To solve logarithmic equations: 1) Use logarithm rules to simplify both sides, 2) Get a single logarithm on each side if possible, 3) Convert to exponential form (if log_a(x) = y, then a^y = x), 4) Solve the resulting equation, 5) Check your answer in the original equation to ensure it's in the domain.
What is the change of base formula and when do I use it?
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The change of base formula is log_b(x) = log_c(x)/log_c(b), where c can be any positive base (usually 10 or e). Use this formula when you need to calculate a logarithm with a base that's not available on your calculator, or when solving equations with different bases.
What's the difference between common logarithms and natural logarithms?
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Common logarithms have base 10 (written as log or log₁₀) while natural logarithms have base e ≈ 2.718 (written as ln). Natural logarithms are used extensively in calculus and exponential growth/decay problems, while common logarithms are often used in scientific applications and pH calculations.
Why can't I take the logarithm of negative numbers?
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Logarithms of negative numbers are undefined in real numbers because no real power of a positive base can equal a negative number. For example, there's no real number x where 10^x = -5. The domain of logarithmic functions includes only positive real numbers.
How do I expand log expressions using logarithm rules?
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To expand logarithms: 1) Use log_a(MN) = log_a(M) + log_a(N) for products, 2) Use log_a(M/N) = log_a(M) - log_a(N) for quotients, 3) Use log_a(M^n) = n·log_a(M) for powers. For example, log₃(x²y/z) = 2log₃(x) + log₃(y) - log₃(z).
What are the most common mistakes when working with logarithms?
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Common logarithm mistakes include: forgetting domain restrictions (arguments must be positive), incorrectly applying rules like log(a+b) ≠ log(a) + log(b), mixing up product and quotient rules, and failing to check solutions in the original equation. Always verify your answers are in the proper domain.
How do logarithms relate to exponential functions?
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Logarithms and exponentials are inverse functions. If y = log_a(x), then a^y = x. This relationship is crucial for solving logarithmic equations by converting them to exponential form. For example, if log₂(x) = 3, then 2³ = x, so x = 8.
More Rules of Logarithms Questions
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