what can you put in place of the ? to make x^2+14x+? a perfect square?

Answer 1

x^2 + 14 x + (14/2)^2

so 49

x^2 + 14 x + 49

= (x+7)^2

if
x^2 + b x
then
x^2 + b x + (b/2)^2
is perfect square