Complete Factorization of P(x) = x^4 + 4x^​2

I'm supposed to find the zeros for the polynomial but i don't know where to start. I'm using a advance college base algebra book thats why i posted on intermidiate, but i guess the problem is a basic problem.
 
Well, the problem only looks complicated and scary because you're not used to factoring quartics (4th-degree polynomials). However, notice that the given polynomial doesn't have any x3, x1 or constant terms. That means that, behind the scenes, it's actually just an ordinary quadratic that you've solved a hundred times before. Try using the substitution u=x2 and rewrite the given polynomial in terms of u. Then factor that much simpler, less daunting polynomial. Don't forget to back-substitute once you get your final u values though, because your teacher doesn't care what values of u satisfy the equation, but wants the corresponding values of x. :)
 
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