Question 980139
{{{5x^2-180=0}}}
{{{x^2-(2*5*18)/5=0}}}
{{{x^2=36}}}
{{{x=0+- 6}}}
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That did not use the Zero Product Rule.  


Here is making use of Zero Product Rule:
{{{5x^2/5-180/5=0}}}
{{{x^2-36=0}}}
{{{x^2-6^2=0}}}
{{{(x-6)(x+6)=0}}}
Either {{{x-6=0}}}  Or  {{{x+6=0}}}
Either x=6  Or  x=-6