ANSWER
[tex]x = - 3[/tex]
EXPLANATION
When a quadratic equation is in the vertex form,
[tex]f(x) = a {(x - h)}^{2} + k[/tex]
the equation of axis of symmetry is simply
[tex]x = h[/tex]
The given quadratic equation is
[tex]f(x) = {(x + 3)}^{2} - 8[/tex]
We can rewrite this as
[tex]f(x) = {(x - - 3)}^{2} - 8[/tex]
We now compare to
[tex]f(x) = a {(x - h)}^{2} + k[/tex]
We have
[tex]h = - 3 \: \: \: and \: \: k = - 8[/tex]
Therefore equation of axis of symmetry is:
[tex]x = - 3[/tex]
