The graph of a quadratic function f(x) = x2 – 6x + 5 is shown here. what is its axis of symmetry?

If you put it in vertex form, it is easy to see the axis of symmetry.

f(x)-5=x^2-6x

f(x)-5+9=x^2-6x+9

f(x)+4=(x-3)^2

f(x)=(x-3)^2-4  so any value of x other than 3 increases the value of f(x), therefore the axis of symmetry is the vertical line x=3.