Question 708520
Try factoring every term and look for the factor set that is common to all the terms.


{{{5x - 15x^3}}}
= {{{5*x - 3*5*x*x*x}}}


WHAT do you see that is common to both terms?  It's the "5x".


= {{{5*x - 5*x*(3x^2)}}}
= {{{5x(1-3x^2)}}}