Question

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

Answer 1

The vertex form:

$y=a(x-h)^2+k\\\\(h,\ k)-vertex$

The axis of symetry is x = h.

$y=ax^2+bx+c\to h=\dfrac{-b}{2a}$

We have

$f(x)=-3x^2+18x-7\to a=-3,\ b=18,\ c=-7$

Substitute:

$h=\dfrac{-18}{(2)(-3)}=\dfrac{-18}{-6}=3$

Answer: x = 3