complex numbers and finding zeros

Question

I need to find all zeros

 

P(x)=x^3+6x^2+12x+16

 

one zero is x=-4

which I then divided the original polynomial by and got

 

x^2+2x+4

 

I input the new quadratic equation into the quadratic formula and ended up with 

 

-1+/-sqrt(12)i

 

The answer I am supposed to come up with is 

 

-1+/- sqrt(3)i

 

I'm not sure how to get the square root three. If someone could do a step by step through the quadratic formula to show me what step I'm missing that would be greatly appreciated

Answer 1

Check your solution from the quadratic formula

 

It should be -1 +/- sqrt(12)/2 i which will simplify to

 

-1+/- sqrt(3) i