Integrating e^f(x): A Simple Explanation and Common Pitfalls

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SUMMARY

The integral of the function \( e^{f(x)} \) with respect to \( x \) cannot be solved without knowing the specific form of \( f(x) \). The discussion highlights that using integration by parts leads to a recursive situation, particularly when \( f(x) \) is a polynomial like \( x^2 \). The proposed method involves setting \( u = e^{f(x)} \) and \( dv = x \, dx \), but this approach does not yield a straightforward solution. Therefore, the ability to integrate \( e^{f(x)} \) is contingent on the characteristics of \( f(x) \).

PREREQUISITES
  • Understanding of integration techniques, specifically integration by parts.
  • Familiarity with exponential functions and their properties.
  • Knowledge of derivatives, particularly \( f'(x) \).
  • Basic calculus concepts, including definite and indefinite integrals.
NEXT STEPS
  • Research the integration of exponential functions with specific forms of \( f(x) \), such as polynomials.
  • Study advanced integration techniques, including reduction formulas and special functions.
  • Learn about the implications of recursive integrals in calculus.
  • Explore the use of numerical methods for approximating integrals that do not have elementary solutions.
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tetris11
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Homework Statement



Hi there, really easy question but I can't get a straight answer online.

What's \intx ef(x) dx

The Attempt at a Solution



I get (ef(x) x)/f'(x) - \int (ef(x))/f'(x) dx

And when I try to do parts on the last component it will proably just go one forever.

Help?
 
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You really won't get a straight answer as that depends on exactly what f(x) is.
You'd need to have u=ef(x) and dv=x dx.

Since you can't integrate ef(x) without knowing what f(x) is. For example if f(x)=x2, then you'd have dv=ex2 dx, which has no elementary integral.
 

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