Question 1044149
.
See also the lesson 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Inequalities/Solving-inequalities-for-polynomials-factored-to-a-product-of-linear-binomials.lesson>Solving inequalities for high degree polynomials factored into a product of linear binomials</A>  

in this site.


By the way, look into the plot of your polynomial


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{{{graph( 330, 330, -5.5, 5.5, -5.5, 5.5,
          x^3-4x
)}}}


<B>Figure</B>. Plot f(x) = {{{x^3-4x}}}

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