I think it's pretty clear once you know that there's an answer. This kind of metagame is pretty useful on contests. You have something that looks like e^(-x^2)

I think it's pretty clear once you know that there's an answer. This kind of metagame is pretty useful on contests. You have something that looks like e^(-x^2) and you know that you need to multiply it by x to get something with an elementary anti-derivative. Other useful tricks are differentiating under the integral sign, building a sequence of integrals (I_n), solving in complex numbers, writing some sort of equation with the value of the integral, and so on.