Question 108988
{{{7x^3-28x=0}}}
{{{x(7x^2-28)=0}}}
x=0 is one solution.
Next solve for 
{{{7x^2-28=0}}}
{{{7x^2=28}}}
{{{x^2=4}}}
{{{x=2}}} and {{{x=-2}}}
The solutions are x=0,-2,2.