Question 1063262
The quadratic expression is factorable.  If you wanted to use Completing the Square, then  the term to add and subtract is  9.


{{{y=x^2+6x+9-7-9}}}
{{{y=x^2+6x+9-16}}}
{{{y=(x+3)^2-16}}}
The vertex is  point  (-3,-16).



{{{(x+3)^2-16=0}}}
{{{(x+3)^2=16}}}
{{{x+3=0+- 4}}}
{{{x=-3+- 4}}}
The x-intercepts are  -7 and +1.