Question 221 of 480
If 6logx2 - 3logx3 = 3log50.2, find x.
- A. 8/3
- B. 4/3
- C. 3/4
- D. 3/8
Correct Answer:
C
Explanation
To solve the equation \( 6\log_x 2 - 3\log_x 3 = 3\log_5 0.2 \), we will break it down step by step.
### Step 1: Simplify the Right Side
First, we need to simplify the right side of the equation, \( 3\log_5 0.2 \). We can rewrite \( 0.2 \) as \( \frac{1}{5} \):
\[
\log_5 0.2 = \log_5 \left(\frac{1}{5}\right) = \log_5 5^{-1} = -1
\]
Thus, we have:
\[
3\log_5 0.2 = 3 \times (-1) = -3
\]
### Step 2: Rewrite the Equation
Now, substituting this back into the original equation gives us:
\[
6\log_x 2 - 3\log_x 3 = -3
\]
### Step 3: Rearranging the Equation
Next, we can rearrange the equation to isolate the logarithmic terms:
\[
6\log_x 2 - 3\log_x 3 + 3 = 0
\]
### Step 4: Factor Out Common Terms
We can factor out the common logarithmic terms:
\[
6\log_x 2 - 3\log_x 3 = 3
\]
Dividing the entire equation by 3 gives:
\[
2\log_x 2 - \log_x 3 = 1
\]
### Step 5: Use Change of Base Formula
Using the change of base formula, we can express the logarithms in terms of base 10 (or natural logarithm):
\[
\log_x 2 = \frac{\log 2}{\log x} \quad \text{and} \quad \log_x 3 = \frac{\log 3}{\log x}
\]
Substituting these into our equation gives:
\[
2\left(\frac{\log 2}{\log x}\right) - \left(\frac{\log 3}{\log x}\right) = 1
\]
### Step 6: Combine the Terms
Combining the terms over a common denominator:
\[
\frac{2\log 2 - \log 3}{\log x} = 1
\]
### Step 7: Solve for \(\log x\)
Now, we can multiply both sides by \(\log x\):
\[
2\log 2 - \log 3 = \log x
\]
### Step 8: Exponentiate to Solve for \(x\)
Exponentiating both sides gives us:
\[
x = 10^{(2\log 2 - \log 3)}
\]
Using properties of logarithms, we can simplify this further:
\[
x = 10^{\log(2^2) - \log 3} = 10^{\log\left(\frac{4}{3}\right)} = \frac{4}{3}
\]
### Conclusion
Thus, the value of \(x\) is:
\[
\boxed{\frac{4}{3}}
\]
### Explanation of Other Options
- **Option A: \( \frac{8}{3} \)**: This value is greater than \( \frac{4}{3} \) and does not satisfy the logarithmic equation derived.
- **Option C: \( \frac{3}{4} \)**: This value is less than \( \frac{4}{3} \) and does not satisfy the logarithmic equation derived.
- **Option D: \( \frac{3}{8} \)**: This value is also less than \( \frac{4}{3} \) and does not satisfy the logarithmic equation derived.
### Revision Summary
- Use the change of base formula to convert logarithms to a common base.
- Rearrange logarithmic equations to isolate terms.
- Combine logarithmic terms over a common denominator.
- Exponentiate to solve for the variable when dealing with logarithmic equations.