1. We are given the equation: $$2 \log(x - 5) = -1 + 2 \log(x + 3)$$
2. The goal is to solve for $x$ exactly.
3. Recall the logarithm property: $$a \log b = \log b^a$$. Using this, rewrite the equation:
$$\log (x - 5)^2 = -1 + \log (x + 3)^2$$
4. Move the constant $-1$ to the left side by rewriting $-1$ as $\log 10^{-1}$ (since $\log 10^{-1} = -1$):
$$\log (x - 5)^2 - \log 10 = \log (x + 3)^2$$
5. Use the logarithm subtraction rule: $$\log a - \log b = \log \frac{a}{b}$$:
$$\log \frac{(x - 5)^2}{10} = \log (x + 3)^2$$
6. Since $\log A = \log B$ implies $A = B$ (for $A,B > 0$), we have:
$$\frac{(x - 5)^2}{10} = (x + 3)^2$$
7. Multiply both sides by 10:
$$\cancel{10} \times \frac{(x - 5)^2}{\cancel{10}} = 10 (x + 3)^2$$
$$ (x - 5)^2 = 10 (x + 3)^2$$
8. Expand both sides:
$$(x - 5)^2 = x^2 - 10x + 25$$
$$(x + 3)^2 = x^2 + 6x + 9$$
9. Substitute expansions:
$$x^2 - 10x + 25 = 10(x^2 + 6x + 9)$$
10. Expand right side:
$$x^2 - 10x + 25 = 10x^2 + 60x + 90$$
11. Bring all terms to one side:
$$x^2 - 10x + 25 - 10x^2 - 60x - 90 = 0$$
12. Simplify:
$$-9x^2 - 70x - 65 = 0$$
13. Multiply both sides by $-1$ to simplify:
$$9x^2 + 70x + 65 = 0$$
14. Use the quadratic formula:
$$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
where $a=9$, $b=70$, $c=65$.
15. Calculate discriminant:
$$\Delta = 70^2 - 4 \times 9 \times 65 = 4900 - 2340 = 2560$$
16. Calculate roots:
$$x = \frac{-70 \pm \sqrt{2560}}{18} = \frac{-70 \pm 16\sqrt{10}}{18}$$
17. Simplify fraction:
$$x = \frac{-35 \pm 8\sqrt{10}}{9}$$
18. Check domain restrictions:
- $x - 5 > 0 \Rightarrow x > 5$
- $x + 3 > 0 \Rightarrow x > -3$
19. Only solutions with $x > 5$ are valid.
20. Evaluate approximate values:
$$x_1 = \frac{-35 + 8\sqrt{10}}{9} \approx \frac{-35 + 25.3}{9} = \frac{-9.7}{9} = -1.08$$ (invalid)
$$x_2 = \frac{-35 - 8\sqrt{10}}{9} \approx \frac{-35 - 25.3}{9} = \frac{-60.3}{9} = -6.7$$ (invalid)
21. No valid solutions satisfy the domain, so the equation has no solution.
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Slug: "log equation"
Subject: "algebra"
Desmos: {"latex":"y=2 \log(x - 5) - 2 \log(x + 3) + 1","features":{"intercepts":true,"extrema":true}}
q_count: 2
Log Equation 958Eb2
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