Question

v^2 - 3v - 40

Answer 1

\[(v-8) (v+5)\]

Answer 2

so,

v = 8
v = -5

Answer 3

see here :
v^2 - 3v - 40 = v^2 - 8v + 5v - 40
= v(v-8) +5(v-8)
= (v+5)(v-8) = 0
hence either v+5 = 0 or v-8 = 0
v=-5 or v=8