Simplify the Expression: (log₄5 + log₄2)/(3log₄2)

Logarithmic Expressions with Change of Base

log⁡45+log⁡423log⁡42= \frac{\log_45+\log_42}{3\log_42}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:11 Let's solve this problem!
00:14 First, we'll apply the log addition rule. We find the log of their product.
00:26 Now, using the power rule of logs, we move the 3 inside the logarithm.
00:36 Next, let's calculate the power.
00:40 We apply the division rule for logarithms.
00:43 Then, find the log of the numerator, using the base of the denominator.
00:48 And that's how we solve this problem. Well done!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

log⁡45+log⁡423log⁡42= \frac{\log_45+\log_42}{3\log_42}=

2

Step-by-step solution

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

  • Step 1: Combine the logarithms in the numerator.
  • Step 2: Simplify the expression using logarithmic properties.

Now, let's work through each step:

Step 1: Combine the logarithms in the numerator using the sum of logarithms property:

log⁡45+log⁡42=log⁡4(5×2)=log⁡410.\log_45 + \log_42 = \log_4(5 \times 2) = \log_4 10.

Step 2: Simplify the entire expression log⁡4103log⁡42\frac{\log_4 10}{3\log_4 2}:

log⁡4103log⁡42=log⁡410log⁡423=log⁡410log⁡48=log⁡810.\frac{\log_4 10}{3 \log_4 2} = \frac{\log_4 10}{\log_4 2^3} = \frac{\log_4 10}{\log_4 8} = \log_8 10.

This follows from the property that log⁡bxlog⁡by=log⁡yx\frac{\log_b x}{\log_b y} = \log_y x.

Therefore, the solution to the problem is log⁡810\log_8 10.

3

Final Answer

log⁡810 \log_810

Key Points to Remember

Essential concepts to master this topic
  • Combine Rule: log⁡ax+log⁡ay=log⁡a(xy) \log_a x + \log_a y = \log_a(xy)
  • Power Rule: 3log⁡42=log⁡423=log⁡48 3\log_4 2 = \log_4 2^3 = \log_4 8
  • Check: Verify log⁡410log⁡48=log⁡810 \frac{\log_4 10}{\log_4 8} = \log_8 10 using change of base ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to apply the power rule to the denominator
    Don't leave 3log⁡42 3\log_4 2 as is = wrong simplification! This misses the key step of converting to log⁡48 \log_4 8 which enables change of base. Always apply the power rule: nlog⁡ab=log⁡abn n\log_a b = \log_a b^n .

Practice Quiz

Test your knowledge with interactive questions

\( \log_75-\log_72= \)

FAQ

Everything you need to know about this question

Why do we use the sum property first?

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The sum property log⁡45+log⁡42=log⁡4(5×2)=log⁡410 \log_4 5 + \log_4 2 = \log_4(5 \times 2) = \log_4 10 combines the numerator into a single logarithm, making the fraction easier to work with.

What is the power rule doing in the denominator?

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The power rule converts 3log⁡42 3\log_4 2 into log⁡423=log⁡48 \log_4 2^3 = \log_4 8 . This is crucial because it allows us to use the change of base formula!

How does log⁡410log⁡48 \frac{\log_4 10}{\log_4 8} become log⁡810 \log_8 10 ?

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This uses the change of base property: log⁡axlog⁡ay=log⁡yx \frac{\log_a x}{\log_a y} = \log_y x . So log⁡410log⁡48=log⁡810 \frac{\log_4 10}{\log_4 8} = \log_8 10 .

Can I solve this without change of base?

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You could use decimal approximations, but that's much harder and less exact. The algebraic approach using logarithm properties gives you the exact answer!

What if I get confused about which base to use?

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Remember the pattern: log⁡axlog⁡ay=log⁡yx \frac{\log_a x}{\log_a y} = \log_y x . The denominator's argument (y) becomes the new base!

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