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## Homework Statement

Show that f'(x) = k/x

## Homework Equations

f is defined from zero to infinity

f(xy) = f(x) + f(y)

f'(1) = k

f(1) = 0

f(x+h) = f(x) + f (1+h/x)

## The Attempt at a Solution

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I know i can write f'(x) = f'(1)/x but thats all I've got so far...