Answer:
x = - 3
Step-by-step explanation:
given a parabola in standard form y = ax² + bx + c (a ≠ 0 )
then the equation of the axis of symmetry is
x = - [tex]\frac{b}{2a}[/tex]
y = x² + 6x - 9 ← is in standard form
with a = 1, b = 6 , then the equation of the axis of symmetry is
x = - [tex]\frac{6}{2}[/tex] = - 3 , that is x = - 3
