f(x) f'(x) puzzle

Enter a trial function f(x) that can depend on up to two parameters a and b.[br][br]The goal is to find a function such that the product of the function and its derivative is constant for all x greater than some x[sub]0[/sub].[br][br]If both x and f(x) are quantities rather than numbers [[b][size=85]see "[i]Semantic Aspects of Quantity[/i]" on the [i]mathMINDhabits[/i] website[/size][/b]] explain how and why this constant can be adjusted.

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