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just a so-called solution

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From an old file in hard disk…

Find f(x) such that

\int_0^x f(t)dt=f(x)-1.

‘solution’

Let \int be “\int_0^x” and f be f(t).

Then

\int f=f-1

1=f-\int f

1=f(1-\int)  (factorization)

f=(1-\int)^{-1}1

Think about sum to infinity, we have

f=(1+\int+\int\int+\int\int\int+\dots)1

=1+\int_0^x1dx+\int_0^x\int_0^x1dx+\int_0^x\int_0^x\int_0^x1dx+\dots

=1+x+\frac{x^2}{2}+\frac{x^3}{6}+\dots

=e^x

done…



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