Write a linear factorization of the function.
f(x) = x4 + 16x2

f(x) = x2 (4x + i)(4x - i)
f(x) = x2 (x + 4i)2
f(x) = x2 (x + 4i)(x - 4i)
f(x) = x2 (4x + i)2