7x^2 -63 =7(x^2 -9)=7(x+3)(x-3)
4x^2 -16 =4(x^2 -4)=4(x+2)(x-2)
(2x+1)^2 -x^2 =4x^2 +4x +1-x^2 =3x^2 +4x +1
=(3x+1)(x+1)
8 4