You can put this solution on YOUR website! For ANY quadratic:
Ax^2 + Bx + C
the axis of symmetry is just:
x = -b/(2a)
(which is from the quadratic equation)
Therefore, for your problem:
Find the axis of symmetry for y = x^2 - 9x +3.
b is -9
a is 1
x = -(-9)/(2*1)
x = 9/2
It is the vertical line that crosses the x-axis at 9/2.