Respuesta :

sqdancefan
The perfect square (x +a)^2 expands to the trinomial x^2 +2ax +a^2

The constant (a^2) is the square of half the x-coefficient.

Your x-coeffficient is 6, so your constant c will be
c = (6/2)^2 = 9 . . . . . . the 3rd choice is appropriate