Question 103071
You are obviously not "totally" stumped as your first step is definitely good.
Factor:
{{{16x^4-40x^2+9 = (4x^2-1)(4x^2-9)}}} Notice that these two factors are the difference of squares. The difference of squares can be factored thus:
{{{A^2-B^2 = (A-B)(A+B)}}} So, applying this to your result, we get:
{{{(4x^2-1)(4x^2-9) = (2x-1)(2x+1)(2x-3)(2x+3)}}}