Question 344305
No, you can't use the quadratic formula on a cubic equation.
Recognize that this is the difference of two cubes. 
{{{x^3-125=(x-5)(x^2+5x+25)=0}}}
One solution is {{{x-5=0}}}
{{{highlight(x=5)}}}
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Now find the root of the quadratic equation with the quadratic formula,
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{x = (-5 +- sqrt( 5^2-4*1*25 ))/2 }}} 
{{{x = (-5 +- sqrt( 25-100 ))/2 }}}
{{{x = (-5 +- sqrt( -75) ))/2 }}}
{{{highlight(x = (5/2)(-1 +- sqrt( 3 )i)) }}}   where {{{i=sqrt(-1)}}}