use completing the square root to solve?

Question

x^2+13x+12=0

the answers I have to choose from are
x=12,x=1
x=-12,x=-13
x=13,x=0
x=12,x=-13
or none of these

Answer 1

(x+6.5)^2-30.25=0
x=-6.5 +- sqrt(30.25)

Answer 2

This factors easily and I can see the answers will be x=-12 or x=-1. To do this by completing the square is a lot of work, but here it goes:

We need to complete the square by adding 1/2 of the 13 and squaring it. We also have to balance by subtracting the same thing.
1/2 of 13 = 13/2, squaring it we get 169/4.

x^2 + 13x + 169/4 + 12 - 169/4 = 0

(x + 13/2)^2 - 121/4 = 0

(x + 13/2)^2 = 121/4, take the sq.rt of both sides:

x + 13/2 = + - 11/2

x = - 13/2 + 11/2 OR x = - 13/2 - 11/2

x = - 2/2 OR x = - 24/2

x = -1 or x = -12

that's it!!!

Answer 3

Okay,
x^2+13x=-12
x^2+13x+(13/2)^2=-12+(13/2)^2
(x+(13/2))^2 = 30.25
sqrt((x+(13/2))^2) = +/-sqrt30.25
x+(13/2) = +/-sqrt30.25
x=+/-sqrt30.25-(13/2)
So, x=-5.5-6.5 = -12
And x=5.5-6.5= -1

I guess its none of these then.