A graph shows the vertex to be at (1.5, 4.75).
The equation of the axis of symmetry is x=1.5.
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If you want to find it analytically, you can put the equation in standard form.
y = -3(x -2)² +4 -(3x -6)
y = -3x^2 +9x -2
This is of the form y = ax² +bx +c with a=-3 and b=9. The axis of symmetry is given by ...
x = -b/(2a) = -9/(2×(-3)) = 3/2 . . . . . same as above
The equation of the axis of symmetry is x=1.5.
_____
If you want to find it analytically, you can put the equation in standard form.
y = -3(x -2)² +4 -(3x -6)
y = -3x^2 +9x -2
This is of the form y = ax² +bx +c with a=-3 and b=9. The axis of symmetry is given by ...
x = -b/(2a) = -9/(2×(-3)) = 3/2 . . . . . same as above