Indefinite Integral involving infinite series

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So in this problem, I think the only way to go is to involve the maclaurin series of exp(x) function in some way so that factors cancel out but i cant figure out how to do so. Please help me with this problem.

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Hints: Start with $f_n(x)^2 + \exp(2x) = (f_n(x) + i \exp(x))(f_n(x) - i \exp(x))$ and use partial fractions. Then use the fact that $x^n/n! = f_n(x) + i \exp(x) - (f_n(x) + i \exp(x))'$.