I'm past this, but couldn't remember the rule....I have

$\displaystyle

\frac {5} {(x+1)^3} < N

$

Then there is a rule for solving this.... You can't multiply both sides by$\displaystyle (x+1)^3$,because you don't know if $\displaystyle x$ is negative or positive. The book says you should get

$\displaystyle

{\sqrt [3]{5/|N|}}

$

Thanks!