Question 59011
factor completely with respect to the intergers 
{{{x^4-13x^2+36}}}
{{{x^4-4x^2-9x^2+36}}}  Replace middle term with two terms that multiply to give you the product of the outer terms: x^4*36=36x^4, but add to give you the middle term:-13x^2.  Then factor by grouping. 
{{{(x^4-4x^2)+(-9x^2+36)}}}
{{{x^2(x^2-4)-9(x^2-4)}}}
{{{(x^2-4)(x^2-9)}}}  Both parenthesese are the differences of perfect squares.
{{{(x+2)(x-2)(x+3)(x-3)}}}
Happy Calculating!!!