(v-3)(v+3)-(v-5)(v+1)=(v²+3v-3v-9)-(v²+v-5v-5)=v²-9-(v²-4v-5)=v²-9-v²+4v+5=
(v²-v²)+4v+(-9+5)=4v-4
v^{2}-9-v^{2}+5v+5-v=4v-4
