Mathematics

Mathematics

Problem

Decide whether the improper integral ∫1∞x+2x3/2+x dx\int_{1}^{\infty} \frac{\sqrt{x}+2}{x^{3/2}+x}\,dx converges or diverges. State your conclusion.
Intuitive explanation

The key is limit comparison: rewrite the integrand by factoring out the dominant term in both numerator and denominator, then compare it to a simpler power function whose convergence you already know. Since x3/2x^{3/2} dominates xx in the denominator for large xx, the integrand behaves like xx3/2=1x\frac{\sqrt{x}}{x^{3/2}} = \frac{1}{x} asymptotically—and you can verify this rigorously using the limit comparison test with g(x)=1xg(x) = \frac{1}{x}.

Intuitive explanation

The key is limit comparison: rewrite the integrand by factoring out the dominant term in both numerator and denominator, then compare it to a simpler power function whose convergence you already know. Since x3/2x^{3/2} dominates xx in the denominator for large xx, the integrand behaves like xx3/2=1x\frac{\sqrt{x}}{x^{3/2}} = \frac{1}{x} asymptotically—and you can verify this rigorously using the limit comparison test with g(x)=1xg(x) = \frac{1}{x}.

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