# Demand function differentiable, prove [pf(p)]'<0 iff p/f(p), f '( p) < -1.(revenue lowers if demand elastic )?

Calculus

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- Anonymous8 years agoBest Answer
[pf(p)]'=p'f(p)+pf'(p)=f(p)+pf'(p)

[pf(p)]'<0 gives

f(p)+pf'(p)< 0

f(p)< - pf'(p)

or

-pf'(p)/f(p) >1

or

multiplying by -1 on both sides

(p/f(p))*f'(p) <-1

i believe thats wat the question was .

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