Answer:
[tex](x^{2} -\sqrt{5} )(x^{2} +\sqrt{5} )(x^{2} +4)[/tex]
Step-by-step explanation:
[tex]x^{4} -x^{2} -20\\if x^{2} =y\\y^{2} -y -20\\y^{2} -5y +4y - 20\\y(y-5)+4(y-5)\\(y-5)(y+4)\\since x^{2} =y\\(x^{2} -5)(x^{2} +4)\\(x^{2} -\sqrt{5} )(x^{2} +\sqrt{5} )(x^{2} +4)[/tex]
