Subjects calculus

Integral Divergence 8C49C9

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1. **State the problem:** Evaluate the improper integral $$\int_0^{+\infty} 2 \ln(x) \, dx$$ and determine if it converges or diverges. 2. **Recall the integral and convergence rules:** The integral involves the natural logarithm function \(\ln(x)\) multiplied by 2. Since the limits are from 0 to infinity, we must check the behavior near 0 and as \(x \to +\infty\). 3. **Rewrite the integral:** $$\int_0^{+\infty} 2 \ln(x) \, dx = 2 \int_0^{+\infty} \ln(x) \, dx$$ 4. **Check convergence near 0:** As \(x \to 0^+\), \(\ln(x) \to -\infty\), so the integral near 0 is improper. Consider the limit: $$\lim_{a \to 0^+} \int_a^1 \ln(x) \, dx$$ 5. **Evaluate \(\int \ln(x) \, dx\):** Use integration by parts: Let \(u = \ln(x)\), \(dv = dx\), then \(du = \frac{1}{x} dx\), \(v = x\). $$\int \ln(x) \, dx = x \ln(x) - \int x \cdot \frac{1}{x} dx = x \ln(x) - \int 1 \, dx = x \ln(x) - x + C$$ 6. **Evaluate the definite integral from \(a\) to 1:** $$\int_a^1 \ln(x) \, dx = [x \ln(x) - x]_a^1 = (1 \cdot \ln(1) - 1) - (a \ln(a) - a) = -1 - (a \ln(a) - a)$$ 7. **Evaluate the limit as \(a \to 0^+\):** Since \(\lim_{a \to 0^+} a \ln(a) = 0\) and \(\lim_{a \to 0^+} a = 0\), $$\lim_{a \to 0^+} (a \ln(a) - a) = 0$$ Therefore, $$\lim_{a \to 0^+} \int_a^1 \ln(x) \, dx = -1$$ 8. **Check convergence near infinity:** Consider the limit: $$\lim_{b \to +\infty} \int_1^b \ln(x) \, dx = \lim_{b \to +\infty} [x \ln(x) - x]_1^b = \lim_{b \to +\infty} (b \ln(b) - b) - (1 \cdot 0 - 1) = \lim_{b \to +\infty} (b \ln(b) - b) + 1$$ Since \(b \ln(b)\) grows faster than \(b\), this limit diverges to infinity. 9. **Conclusion:** The integral diverges because it does not converge at the upper limit. **Final answer:** The integral $$\int_0^{+\infty} 2 \ln(x) \, dx$$ diverges. Hence, the correct choice is **E. Diverges**.