Write a linear factorization of the function.
f(x) = x4+ 9x2
f(x) = x2(x + 3i)(x - 3i)
f(x) = x2(x + 3i)2
f(x) = x2(3x + i)(3x - i)
f(x) = x2(3x + i)
f(x) = x4+ 9x2
f(x) = x2(x + 3i)(x - 3i)
f(x) = x2(x + 3i)2
f(x) = x2(3x + i)(3x - i)
f(x) = x2(3x + i)