Show an integration rule

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Show that $intf'(x)*g(f(x))dx = G(f(x)) + c, G'(x) = g(x)$ (with $f'(x)$ e $G'(x)$ I (obviously) mean that they are the derivatives with respect to the $x$ of the $2$ functions..)

P.S. : use the spoiler when you want to give the solutions so the other people can give their ones..

[Mega-X]

oh yeah try to not derive the $G(f(x))$ function, try to solve only via integration