Notice that:
[tex]\begin{gathered} x^4-25x^2+144=(x^2)^2+(-9-16)x^2+(-9)(-16) \\ =(x^2-9)(x^2-16)\text{.} \end{gathered}[/tex]Now, notice that:
[tex]\begin{gathered} x^2-9=x^2-3^2=(x+3)(x-3), \\ x^2-16=x^2-4^2=(x+4)(x-4)\text{.} \end{gathered}[/tex]Therefore:
[tex]x^4-25x^2+144=(x+3)(x-3)(x+4)(x-4)\text{.}[/tex]Answer:
[tex]x^4-25x^2+144=(x+3)(x-3)(x+4)(x-4)\text{.}[/tex]
