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lim [f(ax)-f(bx)]/x = f'(0)(a-b)

x→0

I feel like this should be really easy, but am I missing something? I tried to use the definition of the derivative, but I know I can't just say f(ax)-f(bx) = (a-b)f(x).

Any ideas?

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# Seemingly Simple Derivative (as a limit) Problem

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