Solve: log₉(e³) × (log₂24 - log₂8) × ln(8×2) | Complete Logarithm Problem

Complex Logarithms with Multiple Base Types

log9e3×(log224log28)(ln8+ln2) \log_9e^3\times(\log_224-\log_28)(\ln8+\ln2)

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:11 We'll use the logarithm subtraction formula, we'll get their logarithm
00:21 We'll use this formula in our exercise
00:31 We'll use the logarithm addition formula, we'll get the logarithm of their product
00:36 We'll use this formula in our exercise
01:01 We'll use the logarithm multiplication formula, we'll switch between the numbers
01:21 We'll use this formula in our exercise
01:36 We'll use the formula to convert from ln to log
01:40 We'll use this formula in our exercise
01:55 Again we'll use the logarithm multiplication formula
02:04 We'll calculate the logarithm and substitute it in the exercise
02:34 We'll calculate this logarithm and substitute it in the exercise
02:59 We'll calculate the final logarithm and substitute it in the exercise
03:09 We'll solve the multiplications
03:19 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

log9e3×(log224log28)(ln8+ln2) \log_9e^3\times(\log_224-\log_28)(\ln8+\ln2)

2

Step-by-step solution

We will solve the problem step by step:

Step 1: Simplify log9e3\log_9 e^3

  • Using the change of base formula, log9e3=lne3ln9\log_9 e^3 = \frac{\ln e^3}{\ln 9}.
  • We know lne3=3lne=3\ln e^3 = 3\ln e = 3, because lne=1\ln e = 1.
  • Thus, log9e3=3ln9=32ln3\log_9 e^3 = \frac{3}{\ln 9} = \frac{3}{2\ln 3}, since ln9=2ln3\ln 9 = 2\ln 3.
  • Therefore, log9e3=32ln3\log_9 e^3 = \frac{3}{2\ln 3}.

Step 2: Simplify log224log28\log_2 24 - \log_2 8

  • Use the logarithm subtraction rule: log224log28=log2(248)=log23\log_2 24 - \log_2 8 = \log_2 \left(\frac{24}{8}\right) = \log_2 3.

Step 3: Simplify ln8+ln2\ln 8 + \ln 2

  • Using the product property of logarithms: ln8+ln2=ln(8×2)=ln16\ln 8 + \ln 2 = \ln(8 \times 2) = \ln 16.
  • Since 16=2416 = 2^4, ln16=4ln2\ln 16 = 4\ln 2.

Step 4: Combine the results

  • We need to check the overall structure: log9e3×log23×4ln2\log_9 e^3 \times \log_2 3 \times 4 \ln 2.
  • Previously calculated: log9e3=32ln3\log_9 e^3 = \frac{3}{2 \ln 3}, log23=ln3ln2\log_2 3 = \frac{\ln 3}{\ln 2}.
  • Therefore, the entire expression becomes:
  • 32ln3×ln3ln2×4ln2=32×4=6\frac{3}{2 \ln 3} \times \frac{\ln 3}{\ln 2} \times 4 \ln 2 = \frac{3}{2} \times 4 = 6.

Therefore, the solution to the problem is 6 6 .

3

Final Answer

6 6

Key Points to Remember

Essential concepts to master this topic
  • Rule: Apply change of base formula for different logarithm bases
  • Technique: Simplify log224log28=log2(24/8)=log23\log_2 24 - \log_2 8 = \log_2(24/8) = \log_2 3
  • Check: Verify 32ln3×ln3ln2×4ln2=6\frac{3}{2\ln 3} \times \frac{\ln 3}{\ln 2} \times 4\ln 2 = 6

Common Mistakes

Avoid these frequent errors
  • Mixing logarithm bases without conversion
    Don't multiply log9e3\log_9 e^3 directly with log23\log_2 3 = wrong result! Different bases can't be combined without conversion. Always convert to common base using change of base formula or natural logarithms.

Practice Quiz

Test your knowledge with interactive questions

\( \log_{10}3+\log_{10}4= \)

FAQ

Everything you need to know about this question

Why can't I just multiply the logarithms with different bases directly?

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Logarithms with different bases represent different mathematical operations! You must convert them to the same base first using the change of base formula: logax=lnxlna\log_a x = \frac{\ln x}{\ln a}.

What's the easiest way to handle multiple logarithm properties at once?

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Work step by step! First use logarithm properties (like logaxlogay=loga(x/y)\log_a x - \log_a y = \log_a(x/y)), then convert bases if needed, and finally multiply the simplified terms.

How do I know when to use the change of base formula?

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Use it whenever you have different bases that need to be combined! Converting everything to natural logarithms (ln\ln) is usually the cleanest approach.

Why does ln(e) equal 1?

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By definition, ln\ln is the natural logarithm with base e. So ln(e)=loge(e)=1\ln(e) = \log_e(e) = 1 because any number to the power of 1 equals itself!

What if I get confused with all the logarithm rules?

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  • Product: log(xy)=logx+logy\log(xy) = \log x + \log y
  • Quotient: log(x/y)=logxlogy\log(x/y) = \log x - \log y
  • Power: log(xn)=nlogx\log(x^n) = n\log x

Practice these three rules and you'll handle most logarithm problems!

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