Solve the Complex Logarithmic Equation: (log_x4 + log_x30.25)/(x*log_x11) + x = 3

Logarithmic Equations with Base Transformations

logx4+logx30.25xlogx11+x=3 \frac{\log_x4+\log_x30.25}{x\log_x11}+x=3

x=? x=\text{?}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find X
00:04 Find the domain
00:17 Use the formula for logical addition, we'll get the log of their product
00:22 Use the power rule for logarithms, move X into the log
00:32 Calculate the product
00:40 Use the formula for logarithmic division
00:44 Get the log of numerator with base denominator
00:59 Solve the log and substitute in the equation
01:14 Group terms and isolate X to find the solution
01:29 Factor the trinomial to find possible solutions
01:34 Check the domain to find the solution
01:37 And this is the solution to the problem

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

logx4+logx30.25xlogx11+x=3 \frac{\log_x4+\log_x30.25}{x\log_x11}+x=3

x=? x=\text{?}

2

Step-by-step solution

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

  • Step 1: Simplify the logarithmic expression logx4+logx30.25\log_x4 + \log_x30.25.
  • Step 2: Use the change of base formula for logarithms.
  • Step 3: Substitute and solve for xx.

Now, let's work through each step:
Step 1: Simplify the logarithmic expression by using the property logx4+logx30.25=logx(4×30.25)\log_x4 + \log_x30.25 = \log_x(4 \times 30.25).
Step 2: Calculate 4×30.25=1214 \times 30.25 = 121, then express as logx121\log_x121.

Step 3: The equation becomes logx121xlogx11+x=3\frac{\log_x121}{x\log_x11} + x = 3. We know logx121=2\log_x121 = 2 when x=11x = 11, thus evaluate the expression with possible values.

Consider a simpler value for xx, like 2. calc log24=2\log_2 4 = 2 and log2121\log_2 121. Using the logarithmic laws further simplifies if appropriate, achieving solution x=2x = 2.

Therefore, the solution to the problem is x=2 x = 2 .

3

Final Answer

2 2

Key Points to Remember

Essential concepts to master this topic
  • Product Rule: Combine logarithms using logxa+logxb=logx(ab) \log_x a + \log_x b = \log_x(ab)
  • Technique: Simplify 4×30.25=121=112 4 \times 30.25 = 121 = 11^2 for easier calculation
  • Check: Substitute x = 2 back: log21212log211+2=3 \frac{\log_2 121}{2\log_2 11} + 2 = 3

Common Mistakes

Avoid these frequent errors
  • Forgetting to combine logarithms before solving
    Don't solve logx4 \log_x 4 and logx30.25 \log_x 30.25 separately = wrong intermediate values! This makes the equation much harder and leads to calculation errors. Always use the product rule to combine: logx4+logx30.25=logx(4×30.25)=logx121 \log_x 4 + \log_x 30.25 = \log_x(4 \times 30.25) = \log_x 121 first.

Practice Quiz

Test your knowledge with interactive questions

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

FAQ

Everything you need to know about this question

Why do we multiply 4 × 30.25 instead of solving each logarithm separately?

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The logarithm product rule says logxa+logxb=logx(ab) \log_x a + \log_x b = \log_x(ab) . This simplifies our equation from two separate logs to just one: logx121 \log_x 121 , making it much easier to solve!

How do I know that 121 = 11²?

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Calculate step by step: 4×30.25=121 4 \times 30.25 = 121 . Then recognize that 11×11=121 11 \times 11 = 121 , so 121=112 121 = 11^2 . This connection helps us see that logx121=2logx11 \log_x 121 = 2\log_x 11 !

What if x = 11 doesn't work in the original equation?

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That's exactly right! When we substitute x = 11, we get division by zero in the denominator. This tells us x = 11 is not a valid solution, so we must try other values like x = 2.

How do I verify that x = 2 is correct?

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Substitute back: log24+log230.252log211+2 \frac{\log_2 4 + \log_2 30.25}{2 \cdot \log_2 11} + 2 . Since log24=2 \log_2 4 = 2 and the entire fraction simplifies to 1, we get 1 + 2 = 3

Can I use the change of base formula to solve this?

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Yes! You can convert to common logarithms: logxa=lnalnx \log_x a = \frac{\ln a}{\ln x} . However, recognizing patterns like 121=112 121 = 11^2 and testing simple values like x = 2 is often faster and more intuitive.

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