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The integral \( \displaystyle\int_{1}^{\infty} \frac{dx}{x^{2}} \) is

  • A.divergent, growing without bound
  • B.convergent, with value \( 1/2 \)
  • C.convergent, with value \( 1 \)
  • D.convergent, with value \( 2 \)

Answer: C

Evaluate to a finite upper limit and then let it grow:

\[ \int_{1}^{t} \frac{dx}{x^{2}} \;=\; \left[-\frac{1}{x}\right]_{1}^{t} \;=\; 1 - \frac{1}{t} \;\longrightarrow\; 1 \quad (t \to \infty). \]

The tail dies fast enough for the total area to be finite, whereas the same integral with \( 1/x \) in place of \( 1/x^{2} \) diverges logarithmically

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