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.

📚Master Logarithmic Laws Through Practice
  • Apply product rule: log_a(MN) = log_a(M) + log_a(N) to solve complex problems
  • 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.

Logarithmic Laws

Constant Values:

It can be automatically determined that:

  • loga(1)=0 log_a\left(1\right)=0
  • loga(a)=1 log_a\left(a\right)=1

Basic Arithmetic Operations

Multiplication, division, subtraction, and addition operations between logarithms:

  • logaMN=logaM+logaN log_aMN=log_aM+log_aN
  • logaM/N=logaMlogaN log_aM/N=log_aM-log_aN
  • Loga(M)×Logn(D)=Logn(M)×Loga(D) Log_a\left(M\right)\times Log_n\left(D\right)=Log_n\left(M\right)\times Log_a\left(D\right)
  • LogaMn=nLogaM Log_aM^n=nLog_aM

Visual explanation of logarithmic rules showing log(x·y) equals log(x) plus log(y), and log(x/y) equals log(x) minus log(y), with arrows connecting each part for clarity.

Changing the Base of a Logarithm:

  • logb(x)=logc(x)/logc(b) log_b\left(x\right)=log_c\left(x\right)/log_c\left(b\right)
  • logb(c)=1/logc(b) log_b\left(c\right)=1/log_c\left(b\right)

Logarithmic change of base formula illustrated: log base b of a equals log base x of a divided by log base x of b, with arrows showing transformation from original form.

Derivative of the Logarithm:

fx=logb(x)fx=1/xln(b) fx=log_b\left(x\right)⇒f^{\prime}x=1/xln(b)

Integral of the Logarithm:

logb(x)dx=x×logb(x)1/ln(b)+C ∫log_b\left(x\right)dx=x\times log_b\left(x\right)-1/ln\left(b\right)+C

Detailed explanation

Practice Rules of Logarithms

Test your knowledge with 38 quizzes

\( \frac{\log_9e^2}{\log_9e}= \)

Examples with solutions for Rules of Logarithms

Step-by-step solutions included
Exercise #1

1log49= \frac{1}{\log_49}=

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • 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 1log49\frac{1}{\log_4 9}.

Step 2: We use the logarithmic property logba=1logab\log_b a = \frac{1}{\log_a b}. Thus, replacing b b with 9 and a a with 4, we have:

1log49=log94\frac{1}{\log_4 9} = \log_9 4.

Step 3: Comparing this result to the provided choices, we find that the correct answer is log94\log_9 4, corresponding to Choice 1.

Therefore, the solution to the problem is log94\log_9 4.

Answer:

log94 \log_94

Video Solution
Exercise #2

2log38= 2\log_38=

Step-by-Step Solution

To solve this problem, let's simplify 2log382\log_3 8 using logarithm rules.

  • Step 1: Recognize the expression form
    The expression is of the form alogbca \cdot \log_b c, where a=2a = 2, b=3b = 3, and c=8c = 8.
  • Step 2: Apply the power property
    According to the power property of logarithms, 2log382 \cdot \log_3 8 can be simplified to log3(82)\log_3 (8^2).
  • Perform the calculation
    Calculate 828^2, which is 6464.
  • Step 3: Simplify further
    Therefore, we have log364\log_3 64.

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 2log382\log_3 8 is log364\log_3 64.

Answer:

log364 \log_364

Video Solution
Exercise #3

log103+log104= \log_{10}3+\log_{10}4=

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(xy)\log_b(x) + \log_b(y) = \log_b(x \cdot y) where both logarithms must have the same base.
  • Step 2: Recognize the base. Here, both logarithms are in base 10: log103\log_{10}3 and log104\log_{10}4.
  • Step 3: Apply the property. Add the two logarithms using the formula: log103+log104=log10(34)\log_{10}3 + \log_{10}4 = \log_{10}(3 \cdot 4).
  • Step 4: Perform the multiplication. Compute 343 \cdot 4 to get 12.
  • Step 5: Express the result as a single logarithm: log1012\log_{10}12.

Therefore, the expression log103+log104\log_{10}3 + \log_{10}4 simplifies to log1012\log_{10}12.

Answer:

log1012 \log_{10}12

Video Solution
Exercise #4

log24+log25= \log_24+\log_25=

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the given expression as log24+log25 \log_2 4 + \log_2 5 .
  • 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 \log_2 4 + \log_2 5 as our expression.

Step 2: Apply the sum of logarithms formula:

log24+log25=log2(45) \log_2 4 + \log_2 5 = \log_2 (4 \cdot 5)

Step 3: Calculate the product:

4×5=20 4 \times 5 = 20

Thus, log2(45)=log220 \log_2 (4 \cdot 5) = \log_2 20 .

Therefore, the solution to the problem is log220 \log_2 20 .

Answer:

log220 \log_220

Video Solution
Exercise #5

log29log23= \log_29-\log_23=

Step-by-Step Solution

To solve the problem of evaluating log29log23\log_2 9 - \log_2 3, we apply the properties of logarithms as follows:

  • Step 1: Recognize that the expression uses a subtraction of logarithms with the same base: log29log23\log_2 9 - \log_2 3.
  • Step 2: Use the logarithmic subtraction rule: logbAlogbB=logb(AB)\log_b A - \log_b B = \log_b \left(\frac{A}{B}\right).
  • Step 3: Simplify using this rule: log29log23=log2(93)\log_2 9 - \log_2 3 = \log_2 \left(\frac{9}{3}\right).
  • Step 4: Perform the division: 93=3\frac{9}{3} = 3.
  • Step 5: Therefore, log2(93)=log23\log_2 \left(\frac{9}{3}\right) = \log_2 3.

Thus, the simplified and evaluated result is log23 \log_2 3 .

Answer:

log23 \log_23

Video Solution

Frequently Asked Questions

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.

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