Improper integrals with parameters

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SUMMARY

The discussion focuses on proving that the limit of the function F(u) = ∫ (u*f(x)/(u² + x²)) dx as u approaches 0 equals f(0), given that f is continuous on the interval [0, ∞] and bounded by M. The user attempts to evaluate the integral by splitting it into two intervals: (0, 1) and (1, ∞), but encounters difficulties with the first term. A suggested approach involves further splitting the first interval into (0, e) and (e, ∞), demonstrating that for any ε > 0, a sufficiently small u leads to the second term approaching zero, thus allowing the limit to be evaluated as ε approaches 0.

PREREQUISITES
  • Understanding of improper integrals and their convergence
  • Familiarity with limits and continuity in calculus
  • Knowledge of integration techniques, particularly with parameters
  • Basic proficiency in handling piecewise functions and intervals
NEXT STEPS
  • Study the properties of improper integrals, specifically focusing on convergence criteria
  • Learn about the Dominated Convergence Theorem and its applications
  • Explore continuity and limits in the context of real analysis
  • Investigate techniques for evaluating integrals with parameters, including substitution methods
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Students and educators in calculus, particularly those dealing with improper integrals and limits, as well as mathematicians interested in advanced integration techniques.

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Homework Statement



Let f be continuous on the interval [0,inf] with abs(f(x)) < M, set
F(u) = \int \frac{u*f(x)}{u^2 + x^2} integral from 0 to inf (bad with latex)

prove that lim F(u) as u --> 0 = f(0)

Homework Equations


none

The Attempt at a Solution



I split the integral into the intervals from (0,1) and (1,inf) since (1,inf) is controlled

now I can't seem to work out the first term. Any help would be great as I'm totally stuck
 
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qualitatively, how about splitting it into (0,e) and (e,inf), then show for any e>0, you can choose u close enough to zero that the 2nd term goes to zero, then consider the limit as e->0 using the continuity of f
 

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