Question 622284
bring everything to one side, factor out an {{{x^2}}} and solve like a normal quadratic. 

basically, this is what you do.

{{{100x^4+400x^3-2100x^2=0}}}
{{{100x^2(x^2+4x-21)=0}}}
{{{100x^2((x^2+7x)+(-3x-21))=0}}}
{{{100x^2(x(x+7)-3(x+7))=0}}} ----> now in this step i noticed that if i factor out an x from the first bracket, and a -3 from the second bracket, then i would end up with an (x+7) as a common factor, so then i could do this:
{{{100x^2(x-3)(x+7)=0}}}
therefore X= -7, 0, and 3