Logarithmic Equation F779De
1. **State the problem:** Solve the equation $$\frac{\ln(-2x)}{5} - 5x = 0$$ for $x$.
2. **Rewrite the equation:** Multiply both sides by 5 to clear the denominator:
$$\ln(-2x) - 25x = 0$$
3. **Isolate the logarithm:**
$$\ln(-2x) = 25x$$
4. **Domain consideration:** The argument of the logarithm must be positive:
$$-2x > 0 \implies x < 0$$
5. **Rewrite the equation using exponentiation:**
Exponentiate both sides to remove the logarithm:
$$-2x = e^{25x}$$
6. **Rewrite as:**
$$-2x = e^{25x}$$
7. **Check for solutions:** This transcendental equation cannot be solved algebraically in closed form. We analyze the function:
$$f(x) = -2x - e^{25x}$$
8. **Check values for $x<0$:**
- At $x=0$, $f(0) = 0 - 1 = -1$ (negative)
- At $x=-0.1$, $f(-0.1) = -2(-0.1) - e^{-2.5} = 0.2 - 0.0821 = 0.1179$ (positive)
Since $f(x)$ changes from positive to negative between $-0.1$ and $0$, there is a root in that interval.
9. **Approximate solution:** Using numerical methods (e.g., bisection), the root is approximately:
$$x \approx -0.044$$
**Final answer:**
$$x \approx -0.044$$