To factor properly this expression, we need to use the next expression for the product of the difference of two squares as follows:
[tex]a^2-b^2=(a+b)\cdot(a-b)[/tex]Since the squares are:
[tex](x^2)^2-(4)^2=(x^2+4)(x^2-4)[/tex]We can also see that we have another difference of two squares in the last part of the expression:
[tex]undefined[/tex]