Question 596272
{{{x^4-5x^2-36}}}


{{{x^4-9x^2+4x^2-36}}} See Note at bottom


{{{(x^4-9x^2)+(4x^2-36)}}}


{{{x^2(x^2-9)+4(x^2-9)}}}


{{{(x^2+4)(x^2-9)}}}


{{{(x^2-9)(x^2+4)}}}


{{{(x-3)(x+3)(x^2+4)}}}


So {{{x^4-5x^2-36}}} completely factors to {{{(x-3)(x+3)(x^2+4)}}}



Note: the numbers -9 and 4 multiply to -36 (the last number) and add to -5 (the second coefficient)