Question

What is the axis of symmetry for f(x) = −5x2 − 20x − 10

Answer 1

for a parabola

\[y = ax^2 + bx + c\]

the axis of symmetry is

\[x = \frac{-b}{2 \times a}\]

in your problem you have a = -5 and b = -20

just substitute and get a value for x, which is the equation of the axis of symmetry

Answer 2

If you are really ambitious, you can "Complete the Square". Same result, of course.

Answer 3

You could also set the derivative = to 0, then solve for x.