Respuesta :

choixongdong
-16r^2+1
= 1 - 16r^2
=(1 +4r)(1 - 4r)
altavistard
I'd suggest you write -16r^2+1 in the equivalent form 1-16r^2.  This makes clearer the fact that -16r^2+1 is the difference of 2 squares.

a^2 - b^2 = (a-b)(a+b)

so   1-16r^2 = (1-4r)(1+4r)  (answer)