Question

Solve by completing the square

5v^2−21=10v

Answer 1

5v^2-10v-21=0

Answer 2

then
the rule
if u have
x^2+bx+c=x^2+bx+(b/2)^2-(b/2)^2+c=0
(x^2+bx+(b/2)^2 )-(b/2)^2 +c=0