Question

What is the axis of symmetry for f(x) = −3x2 + 18x − 7?

Answer 1

The axis of symmetry of a parabola like

$y=ax^2+bx+c$

is a vertical line of the form

$x = k$

where k is the x coordinate of the vertex of the parabola.

In particular, the x coordinate of the vertex of the parabola is given by

$x = -\dfrac{b}{2a}$

which in your case becomes

$x = -\dfrac{18}{-6} = 3$

So, the axis of symmetry is the line

$x=3$