ImSoConfused

2x^4-200x^2      take out the largest common factor  = 2x^2

Divide each of the oeiginal terms by this.....

So we have    2x^4/ 2x^2  =   x^2        and      200x^2// 2x^2   = 100

So  we write  the largest common factor  first, and then, inside a set of parentheses, add the two results we just obtained...and we have

2x^2 ( x^2 + 100)      and that's the factorization