## Calculus (3rd Edition)

$$b)\ 5f'(5x)$$
By the chain rule, we know that $$(f(g(x)))′=f′(g(x))g′(x)$$ In this problem, we let: $$f(x)=f(x) and g(x)=5x$$ And by substituting f(x) and g(x) into the equation, we get: $$f(5x)′=5f′(5x)$$