Logarithmic Equation C1C1Bd
1. **State the problem:** Solve the logarithmic equation $$8 \log_7 (x^2 - 1) - \log_7 5 = 1$$ for $x$.
2. **Recall logarithm properties:**
- $a \log_b c = \log_b c^a$
- $\log_b A - \log_b B = \log_b \left(\frac{A}{B}\right)$
3. **Apply the properties:**
Rewrite the equation as
$$\log_7 (x^2 - 1)^8 - \log_7 5 = 1$$
which becomes
$$\log_7 \left(\frac{(x^2 - 1)^8}{5}\right) = 1$$
4. **Convert logarithmic to exponential form:**
$$\frac{(x^2 - 1)^8}{5} = 7^1 = 7$$
5. **Solve for $x^2 - 1$:**
Multiply both sides by 5:
$$(x^2 - 1)^8 = 35$$
6. **Take the eighth root:**
$$x^2 - 1 = \pm 35^{\frac{1}{8}}$$
7. **Solve for $x^2$:**
$$x^2 = 1 \pm 35^{\frac{1}{8}}$$
8. **Check domain restrictions:**
Since $\log_7 (x^2 - 1)$ is defined only if $x^2 - 1 > 0$, we require
$$x^2 - 1 > 0 \implies x^2 > 1$$
9. **Analyze solutions:**
- For $x^2 = 1 + 35^{\frac{1}{8}}$, this is greater than 1, so valid.
- For $x^2 = 1 - 35^{\frac{1}{8}}$, this is less than or possibly negative, so discard.
10. **Final solutions:**
$$x = \pm \sqrt{1 + 35^{\frac{1}{8}}}$$