I posted this question on the Mathematics Stack Exchange a while ago, and got no responses, so I thought I would ask it here. I'm looking for any real-life applications of integration by substitution where the integrand is unknown as a way of motivating the topic, as opposed to giving repetitive questions which can be answered by typing the integral into WolframAlpha.

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    $\begingroup$ You need a lot of substitution when you learn line integrals, but this is more advanced and not so good for motivation. $\endgroup$ – András Bátkai Jun 12 at 9:07
  • $\begingroup$ I don't think that you should be so wary of Wolfram Alpha danger, when looking for motivational exercises. By nature, they may be simple or even iconic. That's a feature, not a bug. (Even pre-comps, you could make the same stipulation bit with tables versus comps. But you have to realize that for new students, it's NEW in a different way from you.) Remember what is new, interesting to YOU is different than what a neophyte needs. $\endgroup$ – guest Jun 12 at 22:02

This is probably too abstract for students just learning about integration by substitution. But convolution is a "real-world application of integration," finding applications in such things as image processing. One defines

$$(f*g)(t)=\int_{-\infty}^{\infty} f(\tau)g(t-\tau)\, d\tau$$

and then to show $f*g=g*f$ you use integration by substitution.


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