Answer
$$-(4x+1)(4x-5) .$$
Work Step by Step
First, for the polynomial $5 + 16x - 16x^2$, we write $$5 + 16x - 16x^2=-(16x^2-16x-5)=-(16x^2+4x-20x-5) .$$ By grouping the first two terms and the second two terms and then taking out common factors, we have $$-(16x^2+4x-20x-5) =-(4x(4x+1)-5(4x+1))\\ =-(4x+1)(4x-5) .$$