To solve this problem and to calculate the value of the variable "x", you must apply the following proccedure:
1. You have the quadratic equation:
x²+6x+9=12
2. Then:
x²+6x+9-12=0
x²+6x-3=0
3. You must apply the quadratic formula, which is:
(-b±√(b^2-4ac))/2a
a=1
b=6
c=-3
4. Then, the result is:
x=-3±2√3
Therefore, the correct option is the first one: x=-3±2√3