Answer
$4x(x^4+10)(x^4-10)$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $4x^9-400x=\\=4x(x^8-100)\\=4x((x^4)^2-10^2)\\=4x(x^4+10)(x^4-10)$